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Reactivity of a Pd(II) carbene towards 2,6-dimesitylphenyldiazomethane and 2,6-dimesitylphenylazide
Accepted Manuscript Reactivity of a Pd(II) Carbene towards 2,6-dimesitylphenyldiazomethane and 2,6-dimesitylphenylazide Melissa R. Hoffbauer, Cezar C. Comanescu, Vlad M. Iluc PII: DOI: Reference:
S0277-5387(18)30719-8 https://doi.org/10.1016/j.poly.2018.11.002 POLY 13548
To appear in:
Polyhedron
Received Date: Revised Date: Accepted Date:
9 August 2018 29 October 2018 1 November 2018
Please cite this article as: M.R. Hoffbauer, C.C. Comanescu, V.M. Iluc, Reactivity of a Pd(II) Carbene towards 2,6dimesitylphenyldiazomethane and 2,6-dimesitylphenylazide, Polyhedron (2018), doi: https://doi.org/10.1016/ j.poly.2018.11.002
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Reactivity of a Pd(II) Carbene towards 2,6-dimesitylphenyldiazomethane and 2,6dimesitylphenylazide Melissa R. Hoffbauer,† Cezar C. Comanescu, † Vlad M. Iluc* †
equally contributing authors
*
corresponding author
Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556, United States
ABSTRACT The reactivity of a nucleophilic palladium carbene, [{PC(sp2)P}HPd(PMe3)] (1, [PC(sp2)P] = bis[2-(di-iso-propylphosphino)phenyl]methylene), towards 2,6-dimesitylphenyldiazomethane ((dmp)CHN2) and 2,6-dimesitylphenylazide ((dmp)N3) was explored. When treated with (dmp)CHN2, the carbene complex was fully consumed to generate a 3-coordinate Pd(0) complex [{PC(=N–N=CH(dmp))P}HPd(PMe3)] (2), with a newly formed double bond between the backbone carbon and the terminal nitrogen of the diazo compound. Similar reactivity occurred
between
[{PC(sp2)P}HPd(PMe3)]
and
(dmp)N3
to
yield
[{PC(=N–
N=N(dmp))P}HPd(PMe3)] (3); in this instance, there is an interaction between the newly formed C=N moiety and the Pd(0) metal center, resulting in a 4-coordinate distorted tetrahedral complex.
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1. Introduction Late transition metal complexes bearing multiple bonds to main group elements such as C, N, O, S have garnered significant interest in organometallic chemistry due to their role in a variety of biological and chemical processes.[1-3] Beside extensive studies in C-H and C-C activation,[4-6] Bill Jones dedicated a significant amount of his career in inorganic chemistry to studies surrounding a late transition metal sulfido complexes.[7] Despite being unable to isolate and characterize a terminal Ni sulfide complex, evidence supports the transient formation of the Ni=S complex, which paved the way for the synthesis and isolation of late transition metal complexes with multiple bonds to main group elements. Transition metal carbene and imido/nitrene complexes are postulated as intermediates responsible for carbene and nitrogen transfer reactions, such as cyclopropanations and aziridinations, respectively.[8-10] Hence, the synthesis and characterization of transition metal carbene and imido/nitrene complexes have gained substantial interest in order to better understand these processes.[11-14] Organodiazo compounds and organoazides are powerful precursors in the synthesis of transition metal carbene complexes and nitrene/imido complexes, respectively.[15-19] In the presence of a transition metal center, RN2 and RN3 compounds undergo a transformation that results in the extrusion of N2, accompanied by the formation of M-C and M-N complexes with multiple bond character.[20-22] Compounds of this nature are highly reactive and unstable; thus, sterically demanding derivatives can be utilized to increase stability.[23-26] Specifically, 2,6-dimesitylphenyl (2,6-dimesitylphenyl = dmp) derivatives have proven exceptionally useful for the stabilization of both transition metal carbene and imido complexes.[27, 28] For example, Hillhouse et al. reported the synthesis of a 3-coordinate Ni carbene complex employing the bulky dmp functionality, which protected the metal center from participating in
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further reactivity.[29] Additionally, stabilization of the imido functional group has been achieved through utilization of the bulky dmp-substituted azide, (dmp)N3, on several different metal centers (W, Ni, Co, Mo, Ta).[30-35] Also, Deng and coworkers utilized bulky azides, including (dmp)N3, which allowed for the stabilization of a series of low coordinate Co(II) imido complexes. Furthermore, these Co(II) imido complexes were capable of performing nitrene transfer reactions with a variety of different substrates, providing insight into these processes.[36] Despite advancements regarding the synthesis and characterization of late transition metal complexes with multiple bonds to nitrogen and carbon, little work has been done with biscarbene and imido carbene systems. Interestingly, early transition metal centers have proven their competency at supporting such systems, and multiple biscarbene and alkylidene imdo species have been reported.[37-44] Furthermore, most biscarbene or imido carbenes reported on late transition metal centers are those that employ N-heterocyclic carbenes.[27, 45-48], while there is only one example of an early late transition complex containing two nonheteroatom stabilized carbene ligands.[49] Thus, we became interested in the synthesis of a palladium carbene complex bearing a second non-heteroatom stabilized carbene functionality and a palladium carbene complex bearing an imido moiety. Previously, our group reported the synthesis of a nucleophilic Pd(II) carbene complex, [{PC(sp2)P}HPd(PMe3)].[50] Comprehensive reactivity studies with E-H substrates (E-H = NH, O-H, Si-H, and acidic C-H bonds) supported the nucleophilic/basic nature of the anionic carbene carbon.[51-56] Because of the lability of the PMe3 moiety, an empty coordination site can be accessed, making this an attractive system to synthesize group 10 biscarbene and imido carbene complexes. Herein, we report the reactivity of this well-defined Pd(II) carbene system with a bulky diazomethane compound, (dmp)CHN2, as well as a bulky azide, (dmp)N3.
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2. Experimental 2.1. Materials and methods Experiments were performed under a dry nitrogen atmosphere using an MBraun drybox. All solvents were dried by passing through a column of activated alumina, followed by storage over molecular sieves and sodium. Deuterated solvents were obtained from Cambridge Isotope Laboratories. C6D6 was dried by refluxing over dry CaH2 and filtered prior to use and CDCl3 was dried over molecular sieves. NMR spectra were obtained on Bruker 400 and Bruker 500 spectrometers at ambient temperature, unless otherwise noted. All commercial chemicals were used as received, except where specified otherwise. CHN analyses were performed on a CE-440 elemental analyzer or by Midwest Microlab. The diffraction experiments were carried out on a Bruker AXS SMART CCD three-circle diffractometer with a sealed tube using graphite-monochromated Mo-Kα radiation (λ = 0.71073 Å). The crystals were mounted on a plastic loop and used for the diffraction experiments. Anisotropic thermal parameters were refined for all non-hydrogen atoms. The hydrogens were placed according to a riding model. (dmp)CHN2 [57] and (dmp)N3 [35] were synthesized according to previouslypublished literature reports.
2.2. Synthesis of metal complexes 2.2.1.
[{PC(=N-N=CH(dmp))P}HPd(PMe3)]
(2).
In
a
20
mL
scintillation
vial,
[{PC(sp2)P}HPd(PMe3)] (42 mg, 0.074 mmol) and (dmp)CHN2 (26.4 mg, 0.074 mmol) were dissolved in 2 mL of THF and stirred for 2 hours. The volatiles were removed under reduced pressure and the resulting residue was dissolved in THF and passed through a pad of Celite. The solution was concentrated to about 1 mL, layered with n-pentane and left to crystallize at -4-
-35 °C. Yield: 42 mg, 0.045 mmol, 60%. 1H NMR (400 MHz, C6D6) δ 8.74 (s, 1H, ArH), 7.32 (dd, J = 7.1, 1.8 Hz, 2H, ArH), 7.09 – 7.04 (m, 1H, ArH), 6.99 – 6.89 (m, 4H, ArH), 6.84 (s, 1H, ArH), 6.83 (s, 3H, ArH), 6.83 (s, 2H, ArH), 6.77 (d, J = 6.6 Hz, 2H, ArH), 2.46 (s, 2H, CH(CH3)2), 2.31(s, 6H, Me), 2.14 (dd, J = 13.7, 6.0 Hz, 2H, CH(CH3)2), 2.05 (s, 12H, Me), 1.27 (d, J = 3.6 Hz, 9H, PMe3), 1.08 (dt, J = 9.8, 7.0 Hz, 12H, CH(CH3)2), 0.99 (dd, J = 14.5, 7.2 Hz, 6H, CH(CH3)2), 0.76 (dd, J = 13.3, 6.3 Hz, 6H, CH(CH3)2). 31P NMR (162 MHz, C6D6) δ 34.57 (s), -39.44 (s). 13C NMR (101 MHz, C6D6) δ 160.76 (s, ArC), 157.53 (s, ArC), 150.00 – 148.81 (m, ArC), 142.22 (s, ArC), 141.39 (s, ArC), 139.68 (s, ArC), 135.42 (s, ArC), 135.26 (s, ArC), 133.12 (s, ArC), 131.13 (s, ArC), 131.05 – 130.87 (m, Cbackbone), 130.25 (s, ArC), 129.22 (s, ArC), 128.91 (s, ArC), 127.69 (s, ArC), 125.56 (s, ArC), 29.72 (t, J = 8.1 Hz, CH(CH3)2 ), 25.72 (s, CH(CH3)2), 21.91 (d, J = 7.8 Hz, PMe3), 21.40 (s, Me), 21.20 (s, Me), 21.08 – 20.79 (m, CH(CH3)2), 20.70 (s, CH(CH3)2), 20.61 (s, CH(CH3)2), 20.53 (s, CH(CH3)2), 19.40 (s, CH(CH3)2). Anal. Calcd. for C53H71N2P3Pd: C, 68.05; H, 7.65; N, 2.99. Found: C, 68.24; H, 7.83; N 2.63. 2.2.2.
[{PC(=N-N=N(dmp))P}HPd(PMe3)]
(3).
In
a
20
mL
scintillation
vial,
[PC(sp2)P]Pd(PMe3) (36 mg, 0.063 mmol) and (dmp)N3 (23.5 mg, 0.063 mmol) were dissolved in 2 mL of THF and stirred for 2 hours. The volatiles were removed under a reduced pressure and the resulting residue was dissolved in THF and passed through a pad of Celite. The solution was concentrated to about 1 mL, layered with n-pentane and left to crystallize at -35 °C. Yield: 24 mg, 0.025 mmol, 41%. 1H NMR (400 MHz, C6D6) δ 7.14-7.13 (m, 3H, ArH), 7.05 – 6.99 (m, 2H, ArH), 6.97 (s, 3H, ArH), 6.90 (td, J = 7.4, 1.0 Hz, 2H, ArH), 6.85 (d, J = 7.7 Hz, 2H, ArH), 6.82 – 6.78 (m, 4H, ArH), 2.24 (s, 6H, Me), 2.18 (s, 12H, Me), 2.15 – 1.99 (m, 4H, CH(CH3)2), 1.13 (dd, J = 13.3, 5.6 Hz, 6H, CH(CH3)2), 1.08 (dd, J = 10.2, 5.3 Hz, 6H, CH(CH3)2), 0.91 (d, J = 6.2 Hz, 9H, PMe3), 0.91 – 0.82 (m, 6H, CH(CH3)2), 0.68 (dd, J = 15.3, 7.0 Hz, 6H, CH(CH3)2).31P NMR (162 MHz, C6D6) δ 45.52 (d, J = 32.3 Hz), -33.04 (t, J = 32.8
-5-
Hz). 13C NMR (101 MHz, C6D6) δ 156.58 – 155.75 (m, ArC), 150.28 (s, ArC), 140.98 (s, ArC), 139.53 – 138.66 (m, ArC), 136.39 (s, ArC), 134.30 (s, ArC), 133.60 (s, ArC), 130.83 (s, ArC), 130.60 (s, ArC), 130.15 (t, J = 10.9 Hz, Cbackbone), 128.35 (s, ArC), 125.27 (t, J = 2.0 Hz, ArC), 122.87 (s, ArC), 27.54 (t, J = 8.0 Hz, CH(CH3)2), 25.44 (s, CH(CH3)2), 21.78 (s, Me), 21.38 (s, Me), 21.00 (t, J = 3.7 Hz, CH(CH3)2), 20.18 (d, J = 4.1 Hz, CH(CH3)2), 20.09 (d, J = 4.8 Hz, CH(CH3)2), 19.55 (t, J = 5.9 Hz, CH(CH3)2), 18.88 (s, CH(CH3)2). Anal. Calcd. for C52H70N3P3Pd: C, 66.69; H, 7.53; N, 4.49. Found: C, 66.86; H, 7.21; N, 4.39.
3. Results and discussion When [{PC(sp2)P}HPd(PMe3)] was treated with (dmp)CHN2 ((dmp)CHN2 = (2,6dimesitylphenyl)diazomethane), 2 was formed in quantitative yield (equation 1). Crystallographic data for 2 is summarized in Table 1. The solid-state molecular structure of 2 revealed the formation of a C=N between the carbene carbon and the terminal nitrogen in the diazo compound with a distance of 1.289(4) Å. A long distance of 3.44 Å indicates there is no dative interaction between the C=N moiety and the palladium metal center (Pd(1)-N(11) = 3.56 Å). Thus, 2 shows a 3-coordinate trigonal planar geometry at the Pd(0) metal center (sum of the angles = 359.75°). Similarly, a recent report by our group displayed analogous metrical parameters, specifically, when [{PC(sp2)P}HPd(PMe3)] was treated with nitrobenzene, a trigonal planar Pd(0) complex, [{PC(=NOAr)P}HPd(PMe3)], was isolated.[56] In this case, the C=N moiety does not bind to the Pd metal center. Interestingly, our group reported a similar Pd(0) compound, [{PC(=CH2)P}HPd(PMe3)], which was formed through a coupling reaction between [{PC(sp2)P}HPd(PMe3)] and CH2X2 (X = Cl, Br, I).[54] Despite electronic similarities, in the instance of [{PC(=CH2)P}HPd(PMe3)], the newly formed C=CH2 moiety coordinates to the metal center through a side-bound interaction. Formation of the 4-coordinate
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distorted tetrahedral complex was also corroborated by a relatively short distance between the alkene centroid and the palladium metal center.
Mes
P
PMe3 Pd P
H
C
Mes N
N2CH(dmp)
(1)
N P
THF, r.t.
C
Pd
PMe3
P 1
2
All other metrical parameters are as expected. For instance, the N(12) – C(12) distance is representative of an iminemoiety with a distance of 1.275(4) Å. The N(11)-N(12) distance 1.413(3) Å is well in line with a N-N single bond. The 31P{1H} NMR spectrum revealed two broad resonances at 34.57 and -39.44 ppm that represent the equivalent ligand phosphines and the external PMe3 moiety, respectively. Furthermore, the former carbon backbone appears in the
13
C{1H} NMR spectrum at 130.96 ppm as an unresolved multiplet due coupling to
31
P
nuclei. Though this reaction did not yield the desired biscarbene species, the observed reactivity is not unreasonable as the terminal nitrogen within diazo compounds have been determined to be electrophilic.[58, 59] The electrophilic nature of the terminal nitrogen in diazo compounds has been extensively modeled, specifically, Takamura and coworkers treated a variety of diazo compounds with aryl lithium compounds resulting in the formation of aryl hydrazones.[60, 61] Similarly, Hillhouse and coworkers treated (dmp)CHN2 with a strong nucleophile, n-BuLi (nBuLi = n-butyllithium), in the presence of a copper complex to yield a copper species with a terminally bound diazo that had undergone a nucleophilic addition of n-BuLi, rather than the
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desired deprotonation of the acidic hydrogen. Interestingly, when (dmp)CHN 2 was treated with a weak nucleophile, LDA (LDA = lithium di-iso-propylamide), the expected deprotonation of the acidic C-H bond occurred.[57] Thus, the electrophilic nature of the terminal nitrogen in (dmp)CHN2, coupled with the nucleophilic carbene in 1, explains the formation of the C-N bond, rather than the predicted bis carbene complex. Additionally, this reactivity further supports the nucleophilic nature of 1, as no deprotonation of the acidic C-H bond is observed.
Figure 1. Thermal-ellipsoid (50% probability level) representation of 2. Most hydrogen atoms and the solvent molecule were omitted for clarity. Selected distances (Å) and angles (): Pd(1) – P(12) = 2.306(9), Pd(1) – P(11) = 2.307(9), Pd(1) – P(13) = 2.278(9), C(11) – N(11) = 1.275(4), N(11)
-8-
– N(12) = 1.413(3), N(12) – C(12) = 1.275(4), C(12) – C(13) = 1.480(4), Pd(1)-N(11) = 3.589(2), P(11) – Pd(1) – P(13) = 119.99(3), P(11) – Pd(1) – P(12) = 124.05(3), P(12) – Pd(1) – P(13) = 115.61(3).
In an effort to synthesize a carbene imido species, [{PC(sp2)P}HPd(PMe3)] was treated with (dmp)N3 and quantitative conversion to [{PC(=N–N=N(dmp))P}HPd(PMe3)] (3) was observed. Yet again, rather than observing the expected imido complex, a carbon nitrogen bond was formed between the carbene carbon and the terminal azide nitrogen. Crystallographic data for 3 is summarized in Table 1. The solid state molecular structure corroborated this determination with a C(1) – N(11) distance of 1.409(3) Å. The Pd(1)-N(11) distance in complex 3 of 2.500(2) Å is much smaller than the corresponding distance in complex 2 (3.589(2) Å), consistent to the C=N moiety participating in a dative interaction with Pd(0) with a distance of 2.222 Å, generating a 4-coordinate distorted tetrahedral complex ( = 0.52, where represents a square planar geometry and represents a tetrahedral geometry).[62] A series of 4-coordinate Pd(0) species containing a side-bound chalcogenoketone as a ligand ([{PC(=X)P}HPd(PMe3)], X = S, Se, Te), previously reported by our group, were synthesized from [{PC(sp2)P}HPd(PMe3)] and the corresponding elemental chalcogen. Interestingly, the values for these compounds revealed a distorted tetrahedral geometry at the Pd(0) metal center and were determined to exist somewhere between an 2- bound ketone and a chalcogenoketone metallacycle.[56] Bruin and coworkers reported a side bound imine to iridium in which the C-N distance was determined to be 1.407 Å, nearly analogous to the distance within 3; the elongation of the carbon – nitrile imine double bond is attributed to – backdonation from the Ir(I) metal center, but is not considered a formal oxidative addition.[63] This information indicates that 3 exists somewhere between a 2–imine and a metallacycle, also in line with increased –backbonding from the Pd(0) metal center.
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Mes PMe3 P
Pd
N
Mes P
N
N3(dmp)
N
THF, r.t.
C
(2)
P Pd
PMe3
P 1
3
All other metrical parameters for [{PC(=N–N=N(dmp))P}HPd(PMe3)] are as expected, for instance, the Pd-P distances range from 2.28 to 2.31 Å, being within the range of typical Pd(0)-P single bonds.[64-66] The carbon backbone appears in the 13C{1H} NMR spectrum at 130.96 ppm as a triplet (JC-P = 10.9 Hz) that experiences a 3-bond coupling to the equivalent 31
P nuclei. The formation of 3 is relatively unsurprising due to the electrophilic nature of the
azide terminal nitrogen, similar to that of its diazo congener.[67, 68] The electrophilicity of the azide terminal nitrogen has been effectively studied for the Huisgen coupling reaction, also known as a “click cycloaddition”, between azides and alkynes, which results in a controlled cycloaddition generating 5-membered rings.[69] Therefore, the formation of 3 is due to the nucleophilic addition of the carbene moiety to the electrophilic terminal nitrogen of the azide substrate. Despite manipulation of reaction conditions, 3 was the only product isolated from the reaction of 1 with (dmp)N3.
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Figure 3. Thermal-ellipsoid (50% probability level) representation of 3. Most hydrogen atoms and the solvent molecule were omitted for clarity. Selected distances (Å) and angles (): P(11) – Pd(1) = 2.382(7), P(12) – Pd(1) = 2.289(7), P(13) – Pd(1) = 2.380(8), C(1) – N(11) = 1.409(3), N(11) – N(12) = 1.334(3), N(13) – C(108) = 1.404(3), Pd(1) – N(11) = 2.500(2), P(11) – Pd(1) – P(12) = 106.81, P(13) – Pd(1) – C(1)-N(11)centroid = 141.21.
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Table 1. Crystallographic data for 2 and 3. Compound Empirical formula Formula weight Temperature Wavelength Crystal system Space group Unit cell dimensions
Volume Z Density (calculated) Absorption coefficient () F(000) Crystal size range for data collection Index ranges Reflections collected Independent reflections Completeness to = 25.000 Absorption correction Max. and min. transmission Refinement method Data / restraints / parameters Goodness-of-fit on F2: Final R indices [I>2(I)] R indices (all data) Largest diff. peak and hole
2 C53H71N2P3Pd 935.42 120(2) K 0.71073 Å Triclinic P-1 a = 13.1877(6) Å b = 13.4124(6) Å c = 31.2629(14) Å = 86.109(2) = 79.936(2) = 64.2100(18) 4902.1(4) Å3 4 1.267 g·cm-3 0.513 mm-1 1976 0.078 0.075 0.060 mm3 0.662 to 24.999 -14 h 15, -15 k 15, -37 l 37 80022 17271 [Rint = 0.0618] 100.0%
3·½Et2O C108H150N6OP6Pd2 1946.95 120(2) K 1.54178 Å Triclinic P-1 a = 12.6815(3) Å b = 19.1529(4) Å c = 22.1317(5) Å = 100.2530(11) = 102.4840(12) = 92.4070(11) 5146.5(2) Å3 2 1.256 g·cm-3 4.074 mm-1 2060 0.079 0.073 0.070 mm3 2.083 to 68.259 -15 h 15, -23 k 23, -26 l 26 91873 18163 [Rint = 0.0474] 96.4 %
Semi-empirical from equivalents 0.7456 and 0.7081 Full-matrix least-squares on F2 17271 / 0 / 1067
Semi-empirical from equivalents 0.7531 and 0.6148 Full-matrix least-squares on F2
1.091 R1 = 0.0429, wR2 = 0.0940 R1 = 0.0733, wR2 = 0.1018 % 0.967 and -1.615 e-·Å3
1.024 R1 = 0.0364, wR2 = 0.0903 R1 = 0.0438, wR2 = 0.0953 1.102 and -2.229 e-·Å3
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18163 / 0 / 1126
4. Conclusions When [{PC(sp2)P}HPd(PMe3)] was treated with the bulky (dmp)CHN2, the expected biscarbene was not formed, but rather a 3-coordinate trigonal planar Pd(0) complex was generated through the nucleophilic attack of the carbene carbon onto the electrophilic diazo compound. Similarly, when 1 reacted with (dmp)N3, a C-N bond was formed between the electrophilic azide nitrogen and the backbone carbon. However, in the case of 3, the Pd(0) metal center participates in a dative interaction with the newly formed C=N functionality, resulting in a 4-coordinate species. Though the reactions of carbene 1 with (dmp)CHN2 and (dmp)N3 did not result in the hypothesized M=E (E = C or N) moieties, reactivity with these precursors further corroborated the nucleophilic nature of the carbene carbon in [{PC(sp2)P}HPd(PMe3)].
Acknowledgment We thank Dr. Allen Oliver for crystallographic assistance. This work was partially supported by the University of Notre Dame. V.M.I. acknowledges support from the National Science Foundation (NSF) CAREER Program (CHE-1552397). Appendix A. Supplementary material NMR spectra and X-ray data for compounds 2-3. CCDC 1860529-1860530 contain the supplementary crystallographic data for compounds 2-3. These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223336-033; or e-mail: [email protected].
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[36] Y. Liu, J. Du, L. Deng, Inorg. Chem. 56(14) (2017) 8278. [37] M. Fustier, X.-F. Le Goff, M. Lutz, J.C. Slootweg, N. Mézailles, Organometallics 34(1) (2015) 63. [38] I. Elser, W. Frey, K. Wurst, M.R. Buchmeiser, Organometallics 35(24) (2016) 4106. [39] P.P. Samuel, R. Neufeld, K. Chandra Mondal, H.W. Roesky, R. Herbst-Irmer, D. Stalke, S. Demeshko, F. Meyer, V.C. Rojisha, S. De, P. Parameswaran, A.C. Stückl, W. Kaim, J.H. Christian, J.K. Bindra, N.S. Dalal, Chem. Sci. 6(5) (2015) 3148. [40] M.R. Churchill, W.J. Youngs, Inorg. Chem. 18(7) (1979) 1930. [41] F. Basuli, U.J. Kilgore, X. Hu, K. Meyer, M. Pink, J.C. Huffman, D.J. Mindiola, Angew. Chem. Int. Ed. 43(24) (2004) 3156. [42] U.J. Kilgore, J. Tomaszewski, H. Fan, J.C. Huffman, D.J. Mindiola, Organometallics 26(25) (2007) 6132. [43] G. Liu, X. Lu, M. Gagliardo, D.J. Beetstra, A. Meetsma, B. Hessen, Organometallics 27(10) (2008) 2316. [44] M. Gregson, N.F. Chilton, A.-M. Ariciu, F. Tuna, I.F. Crowe, W. Lewis, A.J. Blake, D. Collison, E.J.L. McInnes, R.E.P. Winpenny, S.T. Liddle, Chem. Sci. 7(1) (2016) 155. [45] T.M. Trnka, R.H. Grubbs, Acc. Chem. Res. 34(1) (2001) 18. [46] Y.-S. Meng, Z. Mo, B.-W. Wang, Y.-Q. Zhang, L. Deng, S. Gao, Chem. Sci. 6(12) (2015) 7156. [47] U. Frenzel, T. Weskamp, F. J. Kohl, W.C. Schattenmann, O. Nuyken, W.A. Herrmann, J. Organomet. Chem. 586(2) (1999) 263. [48] N.D. Harrold, A.R. Corcos, G.L. Hillhouse, J. Organomet. Chem. 813 (2016) 46. [49] A.M. LaPointe, R.R. Schrock, W.M. Davis, J. Am. Chem. Soc. 117(17) (1995) 4802. [50] C.C. Comanescu, V.M. Iluc, Organometallics 33(21) (2014) 6059. [51] D.C. Babbini, V.M. Iluc, Organometallics 34(13) (2015) 3141.
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[52] C.C. Comanescu, V.M. Iluc, Organometallics 34(19) (2015) 4684. [53] C.C. Comanescu, V.M. Iluc, Polyhedron (2017). [54] C.C. Comanescu, M. Vyushkova, V.M. Iluc, Chem. Sci. 6(8) (2015) 4570. [55] P. Cui, M.R. Hoffbauer, M. Vyushkova, V.M. Iluc, Chem. Sci. 7(7) (2016) 4444. [56] P.E. Rothstein, C.C. Comanescu, V.M. Iluc, Chem. Eur. J. 23(67) (2017) 16948. [57] V.M. Iluc, C.A. Laskowski, G.L. Hillhouse, Organometallics 28(20) (2009) 6135. [58] M. Zhan, S. Zhang, W.-X. Zhang, Z. Xi, Org. Lett. 15(16) (2013) 4182. [59] M. Regitz, A. Liedhegener, D. Stadler, Justus Liebigs Annalen der Chemie 713(1) (1968) 101. [60] E. Yasui, M. Wada, N. Takamura, Tetrahedron Lett. 47(5) (2006) 743. [61] E. Yasui, M. Wada, N. Takamura, Tetrahedron 65(2) (2009) 461. [62] E.J. Hawrelak, W.H. Bernskoetter, E. Lobkovsky, G.T. Yee, E. Bill, P.J. Chirik, Inorg. Chem. 44(9) (2005) 3103. [63] W.I. Dzik, S.E. Calvo, J.N.H. Reek, M. Lutz, M.A. Ciriano, C. Tejel, D.G.H. Hetterscheid, B. de Bruin, Organometallics 30(3) (2011) 372. [64] B.J. Barrett, V.M. Iluc, Inorg. Chim. Acta 460 (2017) 35. [65] B.J. Barrett, V.M. Iluc, Organometallics 36(3) (2017) 730. [66] C.C. Comanescu, V.M. Iluc, Inorg. Chem. 53(16) (2014) 8517. [67] D. Huang, G. Yan, Adv. Synth. Catal. 359(10) (2017) 1600. [68] S. Bräse, C. Gil, K. Knepper, V. Zimmermann, Angew. Chem. Int. Ed. 44(33) (2005) 5188. [69] R. Huisgen, Angew. Chem. Int. Ed. 2(10) (1963) 565.
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Graphical abstract pictogram:
nucleophilic carbene
PMe3 P dmp C
N
Pd C
P
N
dmp N
H
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N
N
Graphical abstract synopsis
The nucleophilic addition of a well-defined palladium(II) carbene complex to the electrophilic nitrogen atom of 2,6-dimesitylphenyldiazomethane and 2,6dimesitylphenylazide.
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S0277-5387(18)30719-8 https://doi.org/10.1016/j.poly.2018.11.002 POLY 13548
To appear in:
Polyhedron
Received Date: Revised Date: Accepted Date:
9 August 2018 29 October 2018 1 November 2018
Please cite this article as: M.R. Hoffbauer, C.C. Comanescu, V.M. Iluc, Reactivity of a Pd(II) Carbene towards 2,6dimesitylphenyldiazomethane and 2,6-dimesitylphenylazide, Polyhedron (2018), doi: https://doi.org/10.1016/ j.poly.2018.11.002
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Reactivity of a Pd(II) Carbene towards 2,6-dimesitylphenyldiazomethane and 2,6dimesitylphenylazide Melissa R. Hoffbauer,† Cezar C. Comanescu, † Vlad M. Iluc* †
equally contributing authors
*
corresponding author
Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556, United States
ABSTRACT The reactivity of a nucleophilic palladium carbene, [{PC(sp2)P}HPd(PMe3)] (1, [PC(sp2)P] = bis[2-(di-iso-propylphosphino)phenyl]methylene), towards 2,6-dimesitylphenyldiazomethane ((dmp)CHN2) and 2,6-dimesitylphenylazide ((dmp)N3) was explored. When treated with (dmp)CHN2, the carbene complex was fully consumed to generate a 3-coordinate Pd(0) complex [{PC(=N–N=CH(dmp))P}HPd(PMe3)] (2), with a newly formed double bond between the backbone carbon and the terminal nitrogen of the diazo compound. Similar reactivity occurred
between
[{PC(sp2)P}HPd(PMe3)]
and
(dmp)N3
to
yield
[{PC(=N–
N=N(dmp))P}HPd(PMe3)] (3); in this instance, there is an interaction between the newly formed C=N moiety and the Pd(0) metal center, resulting in a 4-coordinate distorted tetrahedral complex.
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1. Introduction Late transition metal complexes bearing multiple bonds to main group elements such as C, N, O, S have garnered significant interest in organometallic chemistry due to their role in a variety of biological and chemical processes.[1-3] Beside extensive studies in C-H and C-C activation,[4-6] Bill Jones dedicated a significant amount of his career in inorganic chemistry to studies surrounding a late transition metal sulfido complexes.[7] Despite being unable to isolate and characterize a terminal Ni sulfide complex, evidence supports the transient formation of the Ni=S complex, which paved the way for the synthesis and isolation of late transition metal complexes with multiple bonds to main group elements. Transition metal carbene and imido/nitrene complexes are postulated as intermediates responsible for carbene and nitrogen transfer reactions, such as cyclopropanations and aziridinations, respectively.[8-10] Hence, the synthesis and characterization of transition metal carbene and imido/nitrene complexes have gained substantial interest in order to better understand these processes.[11-14] Organodiazo compounds and organoazides are powerful precursors in the synthesis of transition metal carbene complexes and nitrene/imido complexes, respectively.[15-19] In the presence of a transition metal center, RN2 and RN3 compounds undergo a transformation that results in the extrusion of N2, accompanied by the formation of M-C and M-N complexes with multiple bond character.[20-22] Compounds of this nature are highly reactive and unstable; thus, sterically demanding derivatives can be utilized to increase stability.[23-26] Specifically, 2,6-dimesitylphenyl (2,6-dimesitylphenyl = dmp) derivatives have proven exceptionally useful for the stabilization of both transition metal carbene and imido complexes.[27, 28] For example, Hillhouse et al. reported the synthesis of a 3-coordinate Ni carbene complex employing the bulky dmp functionality, which protected the metal center from participating in
-2-
further reactivity.[29] Additionally, stabilization of the imido functional group has been achieved through utilization of the bulky dmp-substituted azide, (dmp)N3, on several different metal centers (W, Ni, Co, Mo, Ta).[30-35] Also, Deng and coworkers utilized bulky azides, including (dmp)N3, which allowed for the stabilization of a series of low coordinate Co(II) imido complexes. Furthermore, these Co(II) imido complexes were capable of performing nitrene transfer reactions with a variety of different substrates, providing insight into these processes.[36] Despite advancements regarding the synthesis and characterization of late transition metal complexes with multiple bonds to nitrogen and carbon, little work has been done with biscarbene and imido carbene systems. Interestingly, early transition metal centers have proven their competency at supporting such systems, and multiple biscarbene and alkylidene imdo species have been reported.[37-44] Furthermore, most biscarbene or imido carbenes reported on late transition metal centers are those that employ N-heterocyclic carbenes.[27, 45-48], while there is only one example of an early late transition complex containing two nonheteroatom stabilized carbene ligands.[49] Thus, we became interested in the synthesis of a palladium carbene complex bearing a second non-heteroatom stabilized carbene functionality and a palladium carbene complex bearing an imido moiety. Previously, our group reported the synthesis of a nucleophilic Pd(II) carbene complex, [{PC(sp2)P}HPd(PMe3)].[50] Comprehensive reactivity studies with E-H substrates (E-H = NH, O-H, Si-H, and acidic C-H bonds) supported the nucleophilic/basic nature of the anionic carbene carbon.[51-56] Because of the lability of the PMe3 moiety, an empty coordination site can be accessed, making this an attractive system to synthesize group 10 biscarbene and imido carbene complexes. Herein, we report the reactivity of this well-defined Pd(II) carbene system with a bulky diazomethane compound, (dmp)CHN2, as well as a bulky azide, (dmp)N3.
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2. Experimental 2.1. Materials and methods Experiments were performed under a dry nitrogen atmosphere using an MBraun drybox. All solvents were dried by passing through a column of activated alumina, followed by storage over molecular sieves and sodium. Deuterated solvents were obtained from Cambridge Isotope Laboratories. C6D6 was dried by refluxing over dry CaH2 and filtered prior to use and CDCl3 was dried over molecular sieves. NMR spectra were obtained on Bruker 400 and Bruker 500 spectrometers at ambient temperature, unless otherwise noted. All commercial chemicals were used as received, except where specified otherwise. CHN analyses were performed on a CE-440 elemental analyzer or by Midwest Microlab. The diffraction experiments were carried out on a Bruker AXS SMART CCD three-circle diffractometer with a sealed tube using graphite-monochromated Mo-Kα radiation (λ = 0.71073 Å). The crystals were mounted on a plastic loop and used for the diffraction experiments. Anisotropic thermal parameters were refined for all non-hydrogen atoms. The hydrogens were placed according to a riding model. (dmp)CHN2 [57] and (dmp)N3 [35] were synthesized according to previouslypublished literature reports.
2.2. Synthesis of metal complexes 2.2.1.
[{PC(=N-N=CH(dmp))P}HPd(PMe3)]
(2).
In
a
20
mL
scintillation
vial,
[{PC(sp2)P}HPd(PMe3)] (42 mg, 0.074 mmol) and (dmp)CHN2 (26.4 mg, 0.074 mmol) were dissolved in 2 mL of THF and stirred for 2 hours. The volatiles were removed under reduced pressure and the resulting residue was dissolved in THF and passed through a pad of Celite. The solution was concentrated to about 1 mL, layered with n-pentane and left to crystallize at -4-
-35 °C. Yield: 42 mg, 0.045 mmol, 60%. 1H NMR (400 MHz, C6D6) δ 8.74 (s, 1H, ArH), 7.32 (dd, J = 7.1, 1.8 Hz, 2H, ArH), 7.09 – 7.04 (m, 1H, ArH), 6.99 – 6.89 (m, 4H, ArH), 6.84 (s, 1H, ArH), 6.83 (s, 3H, ArH), 6.83 (s, 2H, ArH), 6.77 (d, J = 6.6 Hz, 2H, ArH), 2.46 (s, 2H, CH(CH3)2), 2.31(s, 6H, Me), 2.14 (dd, J = 13.7, 6.0 Hz, 2H, CH(CH3)2), 2.05 (s, 12H, Me), 1.27 (d, J = 3.6 Hz, 9H, PMe3), 1.08 (dt, J = 9.8, 7.0 Hz, 12H, CH(CH3)2), 0.99 (dd, J = 14.5, 7.2 Hz, 6H, CH(CH3)2), 0.76 (dd, J = 13.3, 6.3 Hz, 6H, CH(CH3)2). 31P NMR (162 MHz, C6D6) δ 34.57 (s), -39.44 (s). 13C NMR (101 MHz, C6D6) δ 160.76 (s, ArC), 157.53 (s, ArC), 150.00 – 148.81 (m, ArC), 142.22 (s, ArC), 141.39 (s, ArC), 139.68 (s, ArC), 135.42 (s, ArC), 135.26 (s, ArC), 133.12 (s, ArC), 131.13 (s, ArC), 131.05 – 130.87 (m, Cbackbone), 130.25 (s, ArC), 129.22 (s, ArC), 128.91 (s, ArC), 127.69 (s, ArC), 125.56 (s, ArC), 29.72 (t, J = 8.1 Hz, CH(CH3)2 ), 25.72 (s, CH(CH3)2), 21.91 (d, J = 7.8 Hz, PMe3), 21.40 (s, Me), 21.20 (s, Me), 21.08 – 20.79 (m, CH(CH3)2), 20.70 (s, CH(CH3)2), 20.61 (s, CH(CH3)2), 20.53 (s, CH(CH3)2), 19.40 (s, CH(CH3)2). Anal. Calcd. for C53H71N2P3Pd: C, 68.05; H, 7.65; N, 2.99. Found: C, 68.24; H, 7.83; N 2.63. 2.2.2.
[{PC(=N-N=N(dmp))P}HPd(PMe3)]
(3).
In
a
20
mL
scintillation
vial,
[PC(sp2)P]Pd(PMe3) (36 mg, 0.063 mmol) and (dmp)N3 (23.5 mg, 0.063 mmol) were dissolved in 2 mL of THF and stirred for 2 hours. The volatiles were removed under a reduced pressure and the resulting residue was dissolved in THF and passed through a pad of Celite. The solution was concentrated to about 1 mL, layered with n-pentane and left to crystallize at -35 °C. Yield: 24 mg, 0.025 mmol, 41%. 1H NMR (400 MHz, C6D6) δ 7.14-7.13 (m, 3H, ArH), 7.05 – 6.99 (m, 2H, ArH), 6.97 (s, 3H, ArH), 6.90 (td, J = 7.4, 1.0 Hz, 2H, ArH), 6.85 (d, J = 7.7 Hz, 2H, ArH), 6.82 – 6.78 (m, 4H, ArH), 2.24 (s, 6H, Me), 2.18 (s, 12H, Me), 2.15 – 1.99 (m, 4H, CH(CH3)2), 1.13 (dd, J = 13.3, 5.6 Hz, 6H, CH(CH3)2), 1.08 (dd, J = 10.2, 5.3 Hz, 6H, CH(CH3)2), 0.91 (d, J = 6.2 Hz, 9H, PMe3), 0.91 – 0.82 (m, 6H, CH(CH3)2), 0.68 (dd, J = 15.3, 7.0 Hz, 6H, CH(CH3)2).31P NMR (162 MHz, C6D6) δ 45.52 (d, J = 32.3 Hz), -33.04 (t, J = 32.8
-5-
Hz). 13C NMR (101 MHz, C6D6) δ 156.58 – 155.75 (m, ArC), 150.28 (s, ArC), 140.98 (s, ArC), 139.53 – 138.66 (m, ArC), 136.39 (s, ArC), 134.30 (s, ArC), 133.60 (s, ArC), 130.83 (s, ArC), 130.60 (s, ArC), 130.15 (t, J = 10.9 Hz, Cbackbone), 128.35 (s, ArC), 125.27 (t, J = 2.0 Hz, ArC), 122.87 (s, ArC), 27.54 (t, J = 8.0 Hz, CH(CH3)2), 25.44 (s, CH(CH3)2), 21.78 (s, Me), 21.38 (s, Me), 21.00 (t, J = 3.7 Hz, CH(CH3)2), 20.18 (d, J = 4.1 Hz, CH(CH3)2), 20.09 (d, J = 4.8 Hz, CH(CH3)2), 19.55 (t, J = 5.9 Hz, CH(CH3)2), 18.88 (s, CH(CH3)2). Anal. Calcd. for C52H70N3P3Pd: C, 66.69; H, 7.53; N, 4.49. Found: C, 66.86; H, 7.21; N, 4.39.
3. Results and discussion When [{PC(sp2)P}HPd(PMe3)] was treated with (dmp)CHN2 ((dmp)CHN2 = (2,6dimesitylphenyl)diazomethane), 2 was formed in quantitative yield (equation 1). Crystallographic data for 2 is summarized in Table 1. The solid-state molecular structure of 2 revealed the formation of a C=N between the carbene carbon and the terminal nitrogen in the diazo compound with a distance of 1.289(4) Å. A long distance of 3.44 Å indicates there is no dative interaction between the C=N moiety and the palladium metal center (Pd(1)-N(11) = 3.56 Å). Thus, 2 shows a 3-coordinate trigonal planar geometry at the Pd(0) metal center (sum of the angles = 359.75°). Similarly, a recent report by our group displayed analogous metrical parameters, specifically, when [{PC(sp2)P}HPd(PMe3)] was treated with nitrobenzene, a trigonal planar Pd(0) complex, [{PC(=NOAr)P}HPd(PMe3)], was isolated.[56] In this case, the C=N moiety does not bind to the Pd metal center. Interestingly, our group reported a similar Pd(0) compound, [{PC(=CH2)P}HPd(PMe3)], which was formed through a coupling reaction between [{PC(sp2)P}HPd(PMe3)] and CH2X2 (X = Cl, Br, I).[54] Despite electronic similarities, in the instance of [{PC(=CH2)P}HPd(PMe3)], the newly formed C=CH2 moiety coordinates to the metal center through a side-bound interaction. Formation of the 4-coordinate
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distorted tetrahedral complex was also corroborated by a relatively short distance between the alkene centroid and the palladium metal center.
Mes
P
PMe3 Pd P
H
C
Mes N
N2CH(dmp)
(1)
N P
THF, r.t.
C
Pd
PMe3
P 1
2
All other metrical parameters are as expected. For instance, the N(12) – C(12) distance is representative of an iminemoiety with a distance of 1.275(4) Å. The N(11)-N(12) distance 1.413(3) Å is well in line with a N-N single bond. The 31P{1H} NMR spectrum revealed two broad resonances at 34.57 and -39.44 ppm that represent the equivalent ligand phosphines and the external PMe3 moiety, respectively. Furthermore, the former carbon backbone appears in the
13
C{1H} NMR spectrum at 130.96 ppm as an unresolved multiplet due coupling to
31
P
nuclei. Though this reaction did not yield the desired biscarbene species, the observed reactivity is not unreasonable as the terminal nitrogen within diazo compounds have been determined to be electrophilic.[58, 59] The electrophilic nature of the terminal nitrogen in diazo compounds has been extensively modeled, specifically, Takamura and coworkers treated a variety of diazo compounds with aryl lithium compounds resulting in the formation of aryl hydrazones.[60, 61] Similarly, Hillhouse and coworkers treated (dmp)CHN2 with a strong nucleophile, n-BuLi (nBuLi = n-butyllithium), in the presence of a copper complex to yield a copper species with a terminally bound diazo that had undergone a nucleophilic addition of n-BuLi, rather than the
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desired deprotonation of the acidic hydrogen. Interestingly, when (dmp)CHN 2 was treated with a weak nucleophile, LDA (LDA = lithium di-iso-propylamide), the expected deprotonation of the acidic C-H bond occurred.[57] Thus, the electrophilic nature of the terminal nitrogen in (dmp)CHN2, coupled with the nucleophilic carbene in 1, explains the formation of the C-N bond, rather than the predicted bis carbene complex. Additionally, this reactivity further supports the nucleophilic nature of 1, as no deprotonation of the acidic C-H bond is observed.
Figure 1. Thermal-ellipsoid (50% probability level) representation of 2. Most hydrogen atoms and the solvent molecule were omitted for clarity. Selected distances (Å) and angles (): Pd(1) – P(12) = 2.306(9), Pd(1) – P(11) = 2.307(9), Pd(1) – P(13) = 2.278(9), C(11) – N(11) = 1.275(4), N(11)
-8-
– N(12) = 1.413(3), N(12) – C(12) = 1.275(4), C(12) – C(13) = 1.480(4), Pd(1)-N(11) = 3.589(2), P(11) – Pd(1) – P(13) = 119.99(3), P(11) – Pd(1) – P(12) = 124.05(3), P(12) – Pd(1) – P(13) = 115.61(3).
In an effort to synthesize a carbene imido species, [{PC(sp2)P}HPd(PMe3)] was treated with (dmp)N3 and quantitative conversion to [{PC(=N–N=N(dmp))P}HPd(PMe3)] (3) was observed. Yet again, rather than observing the expected imido complex, a carbon nitrogen bond was formed between the carbene carbon and the terminal azide nitrogen. Crystallographic data for 3 is summarized in Table 1. The solid state molecular structure corroborated this determination with a C(1) – N(11) distance of 1.409(3) Å. The Pd(1)-N(11) distance in complex 3 of 2.500(2) Å is much smaller than the corresponding distance in complex 2 (3.589(2) Å), consistent to the C=N moiety participating in a dative interaction with Pd(0) with a distance of 2.222 Å, generating a 4-coordinate distorted tetrahedral complex ( = 0.52, where represents a square planar geometry and represents a tetrahedral geometry).[62] A series of 4-coordinate Pd(0) species containing a side-bound chalcogenoketone as a ligand ([{PC(=X)P}HPd(PMe3)], X = S, Se, Te), previously reported by our group, were synthesized from [{PC(sp2)P}HPd(PMe3)] and the corresponding elemental chalcogen. Interestingly, the values for these compounds revealed a distorted tetrahedral geometry at the Pd(0) metal center and were determined to exist somewhere between an 2- bound ketone and a chalcogenoketone metallacycle.[56] Bruin and coworkers reported a side bound imine to iridium in which the C-N distance was determined to be 1.407 Å, nearly analogous to the distance within 3; the elongation of the carbon – nitrile imine double bond is attributed to – backdonation from the Ir(I) metal center, but is not considered a formal oxidative addition.[63] This information indicates that 3 exists somewhere between a 2–imine and a metallacycle, also in line with increased –backbonding from the Pd(0) metal center.
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Mes PMe3 P
Pd
N
Mes P
N
N3(dmp)
N
THF, r.t.
C
(2)
P Pd
PMe3
P 1
3
All other metrical parameters for [{PC(=N–N=N(dmp))P}HPd(PMe3)] are as expected, for instance, the Pd-P distances range from 2.28 to 2.31 Å, being within the range of typical Pd(0)-P single bonds.[64-66] The carbon backbone appears in the 13C{1H} NMR spectrum at 130.96 ppm as a triplet (JC-P = 10.9 Hz) that experiences a 3-bond coupling to the equivalent 31
P nuclei. The formation of 3 is relatively unsurprising due to the electrophilic nature of the
azide terminal nitrogen, similar to that of its diazo congener.[67, 68] The electrophilicity of the azide terminal nitrogen has been effectively studied for the Huisgen coupling reaction, also known as a “click cycloaddition”, between azides and alkynes, which results in a controlled cycloaddition generating 5-membered rings.[69] Therefore, the formation of 3 is due to the nucleophilic addition of the carbene moiety to the electrophilic terminal nitrogen of the azide substrate. Despite manipulation of reaction conditions, 3 was the only product isolated from the reaction of 1 with (dmp)N3.
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Figure 3. Thermal-ellipsoid (50% probability level) representation of 3. Most hydrogen atoms and the solvent molecule were omitted for clarity. Selected distances (Å) and angles (): P(11) – Pd(1) = 2.382(7), P(12) – Pd(1) = 2.289(7), P(13) – Pd(1) = 2.380(8), C(1) – N(11) = 1.409(3), N(11) – N(12) = 1.334(3), N(13) – C(108) = 1.404(3), Pd(1) – N(11) = 2.500(2), P(11) – Pd(1) – P(12) = 106.81, P(13) – Pd(1) – C(1)-N(11)centroid = 141.21.
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Table 1. Crystallographic data for 2 and 3. Compound Empirical formula Formula weight Temperature Wavelength Crystal system Space group Unit cell dimensions
Volume Z Density (calculated) Absorption coefficient () F(000) Crystal size range for data collection Index ranges Reflections collected Independent reflections Completeness to = 25.000 Absorption correction Max. and min. transmission Refinement method Data / restraints / parameters Goodness-of-fit on F2: Final R indices [I>2(I)] R indices (all data) Largest diff. peak and hole
2 C53H71N2P3Pd 935.42 120(2) K 0.71073 Å Triclinic P-1 a = 13.1877(6) Å b = 13.4124(6) Å c = 31.2629(14) Å = 86.109(2) = 79.936(2) = 64.2100(18) 4902.1(4) Å3 4 1.267 g·cm-3 0.513 mm-1 1976 0.078 0.075 0.060 mm3 0.662 to 24.999 -14 h 15, -15 k 15, -37 l 37 80022 17271 [Rint = 0.0618] 100.0%
3·½Et2O C108H150N6OP6Pd2 1946.95 120(2) K 1.54178 Å Triclinic P-1 a = 12.6815(3) Å b = 19.1529(4) Å c = 22.1317(5) Å = 100.2530(11) = 102.4840(12) = 92.4070(11) 5146.5(2) Å3 2 1.256 g·cm-3 4.074 mm-1 2060 0.079 0.073 0.070 mm3 2.083 to 68.259 -15 h 15, -23 k 23, -26 l 26 91873 18163 [Rint = 0.0474] 96.4 %
Semi-empirical from equivalents 0.7456 and 0.7081 Full-matrix least-squares on F2 17271 / 0 / 1067
Semi-empirical from equivalents 0.7531 and 0.6148 Full-matrix least-squares on F2
1.091 R1 = 0.0429, wR2 = 0.0940 R1 = 0.0733, wR2 = 0.1018 % 0.967 and -1.615 e-·Å3
1.024 R1 = 0.0364, wR2 = 0.0903 R1 = 0.0438, wR2 = 0.0953 1.102 and -2.229 e-·Å3
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18163 / 0 / 1126
4. Conclusions When [{PC(sp2)P}HPd(PMe3)] was treated with the bulky (dmp)CHN2, the expected biscarbene was not formed, but rather a 3-coordinate trigonal planar Pd(0) complex was generated through the nucleophilic attack of the carbene carbon onto the electrophilic diazo compound. Similarly, when 1 reacted with (dmp)N3, a C-N bond was formed between the electrophilic azide nitrogen and the backbone carbon. However, in the case of 3, the Pd(0) metal center participates in a dative interaction with the newly formed C=N functionality, resulting in a 4-coordinate species. Though the reactions of carbene 1 with (dmp)CHN2 and (dmp)N3 did not result in the hypothesized M=E (E = C or N) moieties, reactivity with these precursors further corroborated the nucleophilic nature of the carbene carbon in [{PC(sp2)P}HPd(PMe3)].
Acknowledgment We thank Dr. Allen Oliver for crystallographic assistance. This work was partially supported by the University of Notre Dame. V.M.I. acknowledges support from the National Science Foundation (NSF) CAREER Program (CHE-1552397). Appendix A. Supplementary material NMR spectra and X-ray data for compounds 2-3. CCDC 1860529-1860530 contain the supplementary crystallographic data for compounds 2-3. These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223336-033; or e-mail: [email protected].
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Graphical abstract pictogram:
nucleophilic carbene
PMe3 P dmp C
N
Pd C
P
N
dmp N
H
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N
N
Graphical abstract synopsis
The nucleophilic addition of a well-defined palladium(II) carbene complex to the electrophilic nitrogen atom of 2,6-dimesitylphenyldiazomethane and 2,6dimesitylphenylazide.
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