Reactivity of palladium olefin complexes with heteroditopic NHC–pyridine as spectator ligand toward olefin exchange

Inorganica Chimica Acta 421 (2014) 326–334

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Reactivity of palladium olefin complexes with heteroditopic NHC–pyridine as spectator ligand toward olefin exchange Luciano Canovese ⇑, Fabiano Visentin, Claudio Santo Dept. Molecular Sciences and Nanosystems, University Ca’ Foscari, Venice, Italy

a r t i c l e

i n f o

Article history: Received 14 May 2014 Received in revised form 18 June 2014 Accepted 23 June 2014 Available online 2 July 2014 Keywords: Palladium(0) olefin complexes Olefin exchange equilibria Strong r-donor ligands Hemilabile carbene–pyridine

a b s t r a c t We have synthesized some derivatives bearing two strong r-donor ligands simultaneously coordinated to the palladium centre by exploiting the lability of the pyridine wing of the (1-methyl-3-((6-methylpyridine-2-yl)methyl)-imidazole) (Me-NHC-CH2-Py) moiety as a spectator ligand in Pd(0) complexes stabilized by deactivated olefins. Unprecedented mixed complexes bearing the ligand L (L = triphenylphosphine (PPh3), 2,6-dimethylphenyl isocyanide (DIC), triethyl phosphite (P(OEt)3)) and the ligand Me–NHC–CH2–Py with the uncoordinated dangling pyridine wing were therefore obtained by reacting an equimolar amount of the ligands L with the complex [Pd(g2-olefin)(Me–NHC–CH2–Py)] (olefin = tetramethylethenetetracarboxylate (tmetc), fumaronitrile (fn), maleic anhydride (ma), naphthoquinone (nq)). Moreover, we have determined the equilibrium constants KE(ol) for the olefin exchange in the complex [Pd(g2-olefin)(Me–NHC–CH2–Py)] and the related olefin coordinative ability order. Ó 2014 Elsevier B.V. All rights reserved.

1. Introduction Pd(0) olefin complexes are often identified as the active catalytic or pre-catalytic species in a variety of cross-coupling reactions [1]. In this respect they represent a very important class of widely studied compounds [2]. Notably, in addition to the oxidation state of the metal and the nature of the olefin, the structure of the spectator ligands is very important in determining the performance of the catalysts. For instance, the hemilabile ligands [3] due to their tightly coordinated pivot can ensure the stability of the catalyst, guarantee the activation of a pre-defined molecular site by decoordination of the labile wing and eventually restore the original molecular structure by its re-coordination [4]. Moreover, the labile coordinating wing can be easily substituted by numerous nucleophiles which can modulate the steric and electronic characteristics of the ensuing complexes on the basis of the researchers’ target. Among the number of heteroditopic ligands, the bidentate carbene derivatives NHC–E (donor atom E = P, N, O, S) [5] play an important role owing to the stability toward heat, moisture, air and the versatility imparted to their derivatives. Furthermore, NHC–E (E = O, N, S) palladium complexes, as a consequence of the easy displacement of the labile coordinating atom, can be used in the facile synthesis of complexes bearing mixed spectator ligands. In particular, we have recently studied the reactivity of some Pd(II) complexes ⇑ Corresponding author. Tel.: +39 041 2348655. E-mail address: [email protected] (L. Canovese). http://dx.doi.org/10.1016/j.ica.2014.06.017 0020-1693/Ó 2014 Elsevier B.V. All rights reserved.

bearing the same or different strong coordinating moieties such as NHC, phosphines, phosphites and isocyanides [6]. Similar Pd(0) species are less common [7] whereas, at the best of our knowledge, no Pd(0) g2-olefin derivatives were synthesized. Therefore, we have carried out the synthesis of palladium olefin complexes bearing two different strong coordinating ligands taking advantage of the peculiar nature of the hemilabile (1-methyl-3-((6-methylpyridine-2-yl)methyl)-imidazole) (Me–NHC–CH2–Py) moiety. The complexes prepared, the synthetic strategy and the adopted numbering scheme are reported in the following Scheme 1, where complex 2b and all the type 3–5 derivatives are newly synthesized compounds.

2. Result and discussion 2.1. Synthesis of type 2 complexes On the basis of published strategies, we have first synthesized the (1-methyl-3-((6-methylpyridine-2-yl)methyl)-imidazol-3ium) bromide salt (Me–NHC–CH2–PyHBr) which was used in the synthesis of type 2 complexes [8]. In particular, the new substrate 2b was obtained by reacting the silver derivative [Me–NHC–CH2– PyAgBr] synthesized according to Elsevier [5g,9] with the 2methyl-6-(phenylthiomethylpyridine)palladium fumaronitrile derivative 1b, synthesized as reported in Refs. [10,11]. Remarkably, the above reported protocol gives the complexes of type 2 in good yield since precipitation of AgBr is evident and

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O MeOOC

O

COOMe ;

NC

;

; O

MeOOC

COOMe

tetramethylethenetetracarboxylate tmetc (a)

N

O O maleic anhydride ma (c)

CN f umaronitrile f n (b)

naphthoquinone nq (d)

N

N

N

N AgBr

Pd

N

S

Pd

olefin

[Me-NHC-CH2-Py AgBrl]

olef in = tmetc; 1a olef in= fn; 1b olef in = ma; 1c olef in= nq; 1d

olef in = tmetc; 2a olef in = fn; 2b olef in = ma; 2c olef in = nq; 2d

4

5

3 N

N

Pd

N

N

L

6 N

N

Pd

olefin

N

olefin

L

olefin 3, 4, 5

2

L = PPh3; olef in = tmetc, f n, ma, nq; 3a, 3b, 3c, 3d L= DIC; olef in = tmetc, f n, ma; 4a, 4b, 4c L= P(OEt) 3; olefin = tmetc, f n, ma; 5a, 5b, 5c Scheme 1. Olefins, synthetic protocol for the Pd(0) complexes and the adopted numbering scheme.

forces the reaction to completion, thereby rendering such a protocol versatile, efficient and easy to exploit. Moreover, in this case, the described strategy is imposed by the incompatibility among the strong bases, generally used for the formation in solution of the free carbene and the Me–NHC–CH2–Py imidazolium salt that might undergo deprotonation at the CH2N group. The obtained new complex 2b was eventually characterized by means of its 1H and 13C NMR spectra and elemental analysis. As can be seen in Fig. 1 all the signals of the ligand in complex 2b are shifted with respect to those of the silver derivatives to variable extents and, as a consequence of the diastereotopicity induced by the coordination of fumaronirile, the CH2Py protons resonate as an AB system within 5.10 and 5.26 ppm. The olefin protons, due to the back donation promoted by the metal in low oxidation state, shift upfield by ca. 3.5 ppm with respect to those of the free olefin. Similarly, the olefin carbons undergo a marked upfield shift as well (ca. 100 ppm) and resonate at 15.2 and 17.7 ppm. 2.2. Determination of the equilibrium constant for the olefins exchange in type 2 complexes As a part of our ongoing research, we are particularly interested in the influence of the ancillary ligands on the stability of Pd(0) olefin derivatives which we have assessed by measuring the equilib-

rium constant of the direct exchange between olefins according to the following reaction [12]:

½Pdðg2 -olefin1 ÞðL—L0 Þ þ olefin2 ½Pdðg2 -olefin2 ÞðL—L0 Þ þ olefin1

ð1Þ

The overall results summarizing the coordinative capabilities of the electron poor olefins as a function of their structural and electronic features and of the nature of the ancillary ligands were published [12c] and eventually inserted in a review dealing with Pd(0) olefin derivatives bearing labile and hemilabile ancillary ligands [13]. In order to determine the relative thermodynamic stability of the complexes bearing the spectator ligand Me–NHC–CH2–Py, we have determined the equilibrium constant KE(ol) of the exchange reaction between the complex 2d with the olefins ma, fn and tmetc (Eq. (1)). The reaction of complex 2d (chosen as the reference substrate because of its favourable UV–Vis spectrum and related absorbance changes), and the less hindered olefins ma and fn, is an immediate process at RT and allows the direct titration of the complex in CHCl3 by addition of microaliquots of the entering olefins at adequate concentrations. An example of absorbance changes as a function of the concentration of the titrant and a non linear regression analysis of the titration data are reported in Figs. 2 and 3, respectively. The determination of KE(tmetc), related to the equilibrium between the complex 2d reacting with the hindered tmetc olefin

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Fig. 1. 1H NMR spectra of the complexes 2b (below) and [Me–NHC–CH2–PyAgCl] (above) (CDCl3, 298 K).

eral minutes. Therefore, we first measured the rate of the forward exchange reaction by reacting complex 2d with tmetc by using an olefin concentration range that in any case would ensure the complete displacement of the olefin nq ([tmetc]0:[2d]0 = (1550):1) by means of non linear regression analysis of the monoexponential function:

At  A1 ¼ ðA0  A1 Þekobs t

Fig. 2. Absorbance changes for the equilibrium reaction: 2d + fn = 2b + nq in CHCl3 at 298 K.

Fig. 3. Non linear regression analysis for the 2d + ma = 2c + nq, in CHCl3 at 298 K and k = 400 nm.

equilibrium

reaction

and the complex 2a, was achieved by means of a different approach since the exchange reaction between olefins takes sev-

ð2Þ

where At was the time dependent absorbance value, whereas the initial absorbance A0, the final A1 and the pseudo-first order rate constant kobs represent the parameters to be optimized. The straight line resulting from the linear regression analysis of kobs versus [tmetc] displays a statistically unsignificant intercept and a slope which represents the second order rate constant of the forward reaction (kf = 0.77 ± 0.03 mol1 dm3 s1). An example of non linear regression analysis in the case of the forward reaction (substitution of nq), and the overall linear regression analysis are reported in Figs. S1 and S2 (Supplementary material), respectively. The reverse displacement of the olefin tmetc from the complex 2a by nq was also studied under similar experimental conditions. From non linear regression analysis and the related linear regression it was possible to determine the value of the reverse second order rate constant kr = 4.3 ± 0.2 mol1 dm3 s1. Thus, the equilibrium constant KE(tmetc) for the exchange reaction 2d + tmetc = 2a + nq was calculated as kf/kr = 0.18 ± 0.01. Notably, the temperature dependence of kr was also measured and the Eyring linear regression allows the estimate of DH# and DS# for the reverse reaction. In Supplementary material the kr values as a function of the temperature and the Eyring linear regression are reported in Tab. S1 and Fig. S3, respectively. The ensuing activation parameters are DH# = 13 ± 1 kcal mol1 and DS# = 12.0 ± 3.6 cal mol1 K1 where the negative value of the activation entropy points to an associative transition state in which both the entering and the leaving olefins are simultaneously coordinated to palladium. In the following Table 1 we report the final KE values measured as described above. The coordinative ability order and the measured values of the equilibrium constants KE(ol) in Table 1 are both in accord with similar data for complexes bearing a number of different spectator ligands [6,12]. The coordinative ability order of the olefins was in fact confirmed since without exception it is ma > fn > tmetc. However, the ratio between equilibrium constants of Tab. 1 (KE(ma)/KE(fn) = 4.8, KE(fn)/KE(tmetc) = 17.8), deserves some comments.

L. Canovese et al. / Inorganica Chimica Acta 421 (2014) 326–334 Table 1 KE(ol) values determined in CHCl3 at 298 K for the reaction: 2d + olefin = 2 + nq (2 = 2c, 2b, 2a). olefin

KE(ol)

ma fn tmetc

15.4 ± 0.4 3.2 ± 0.2 0.18 ± 0.01

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the olefin itself. Finally, the increased coordinative ability of ma vs. fn (KE(ma)/KE(fn) = 4.8 versus KE(ma)/KE(fn) = 3.06 in Ref. [11]) is probably due to the stabilization induced by the more electron withdrawing ma in complexes of the metal in low oxidation state bearing strong r donor ligands. In any case such a value for KE(ma)/ KE(fn) (4.8) represents the highest KE(ma)/KE(fn) ratio ever measured, irrespectively of the ancillary ligands. 2.3. Synthesis of type 3 complexes

In fact, the value of 17.8, although unusually high, is not unprecedented since a similar ratio (20) was found in systems bearing spectator ligands with similar steric structure [11]. It was shown that a methyl group in position 6 of the pyridine in 2(t-butylthiomethyl)pyridine distorts the main plane of the related palladium complexes [14]. The ligand Me–NHC–CH2–Py has a molecular structure very similar to that of the above cited complexes since it displays a methyl substituent in the imidazole ring. Thus, the hindered tmetc is more easily displaced when coordinated to distorted complexes, probably thanks to steric interferences between the methyl group of the spectator ligand and one COOMe group of

Fig. 4. 1H NMR (a),

13

Finally, taking advantage of the lability of the pyridine wing we have synthesized the new complexes 3–5 by reacting the substrates 2 with an equimolar amount of triphenylphosphine (PPh3), 2,6-dimethylphenyl isocyanide (DIC) and triethyl phosphite P(OEt)3, respectively (Scheme 1). As for a general discussion about the complexes bearing mixed spectator ligands 3–5 it is noteworthy that: (i) Only the olefin complexes of type 3 (L = PPh3) can be synthesized and characterized.

C NMR (b), spectra of complex 3a in CDCl3 at 298 K.

Fig. 5. 1H NMR spectra of complex 5a in CD2Cl2 at 243 K (below) and 298 K (above).

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(ii) The derivatives bearing the bulky tmetc coordinated were isolated as remarkably pure independently of the nature of L. (iii) Among the naphthoquinone derivatives only the complex 3d (L = PPh3) is stable enough to be isolated and fully characterized. In all the other cases a massive decomposition is observed and no pure species can be isolated even at low temperature. (iv) The complexes bearing the less hindered olefins fn and ma (4b, 4c and 5b, 5c) co-precipitate with a significant amount (10%) of the two homoleptic compounds ([Pd(Me–NHC– CH2–Py)2ol] and [PdL2ol]) as a consequence of the rapid ancillary ligand exchange in solution. Apparently, the difference in the thermodynamic stability among the involved species and the activation energy of the interconversion are low, so that an equilibrium among all the statistically possible species is rapidly established [12b].

range 28.9 and 34.4 ppm i.e. about 40 ppm downfield with respect to free phosphine. Similarly, the coordinated phosphite resonates in complexes 5 within 144.4 and 147.8 ppm whereas the methyl substituents of the isocyanide in complexes 4 resonate in the interval 2.18–2.32 ppm i.e. within 0.2 and 0.34 ppm upfield of the free ligand. Finally, the olefin signals of all the studied complexes undergo an upfield shift of about 3–3.5 and 90–100 ppm in the case the 1H and 13C resonances, respectively. For the sake of clarity it is now convenient to discuss the solution behaviour of the complexes bearing the same olefin. As can be seen in Fig. 4, the 1H and 13C NMR signals of the methyl groups and the olefin carbons of the tmetc of complex 3a, resonate as four independent singlets within 3.24 and 3.52 and within 51.4 and 52.6 ppm, respectively. This phenomenon is probably due to the hampered rotation of the ligand Me–NHC–CH2–Py about the Pd–C bond due to the PPh3 bulkiness, as already observed [8b,15]. At variance, the methyl signals of the complexes 4a and 5a are recorded as a couple of singlets at 3.63, 3.71 and 351, 3.60 ppm, respectively. Apparently, the steric interference described above is not observed in the RT NMR spectra of the less hindered derivatives 4a and 5a although, as can be seen in Fig. 5 the rotation of the Me–NHC– CH2–Py fragment in these complexes can also be easily frozen by lowering the temperature.

From the NMR spectra of the complexes obtained upon addition of L (L = PPh3, P(OEt)3, DIC) to type 2 complexes, the displacement of the pyridine wing is confirmed by the upfield shift (Dd = 1– 1.2 ppm) of the H6 pyridine proton, whereas the coordinated ligands L resonate at remarkably different frequencies from those of the uncoordinated ones. Thus, the 31P NMR spectra of the complexes 3 display the signal of the coordinated phosphine in the

(a)

(b)

N

N

L

N

L CN

NC

Pd

P Pd

N

N CN NC

N

Fig. 6. (a) Possible diastereoisomers in the case of the fumaronitrile derivatives 3b, 4b and 5b. (b) temperatures.

(a)

31

P NMR of complex 3b spectra recorded in CD2Cl2 at different

(b)

N

N

O N

O

N

Pd P

P Pd L

N

enndo o

O

O

N

L

ex exo

Fig. 7. (a) endo and exo isomers in complexes of type 3. 1H and

31

P NMR spectra of complex 3d recorded in CD2Cl2 at 243 K.

L. Canovese et al. / Inorganica Chimica Acta 421 (2014) 326–334

In the case of the derivatives of E-olefin fumaronitrile (3b, 4b, 5b) the hampered rotation of the carbene fragment should generate two diastereoisomers in solution. Once again, the existence of two diastereoisomers can be clearly observed for instance in the case of the 31P NMR spectra of the complex 3b recorded at low temperature (Fig. 6) althoughh, the existence of the isomers is generally not observed at RT (see for instance Figs. S4 and S5 in Supplementary material). Complexes 3c, 4c, 5c and 3d are derivatives of the type Z-olefins maleic anhydride and naphthoquinone, respectively. Owing to the position of the dangling pyridine they can exist as exo and endo isomers and in the case of the most hindered complex 3d, the presence of the isomers is observed in the low temperature NMR spectra (Fig. 7). Also in this case, rotation about the Pd–C bond of the Me–NHC–CH2–Py ligand justifies the fluxionality observed at RT. 3. Conclusions We have synthesized four olefin Pd(0) complexes bearing the (1-methyl-3-((6-methylpyridine-2-yl)methyl)-imidazole) (Me– NHC–CH2–Py) moiety as spectator ligand. Taking advantage of the hemilability of the pyridine wing of the ligand, we have obtained several Pd(0) olefin complexes in which the ligands phosphine, phosphite and isocyanide are coordinated to palladium together with the potentially bidentate Me–NHC–CH2–Py ligand bearing an uncoordinated pyridine in its dangling wing. All the new complexes with two strong ligands concomitantly coordinated were fully characterized by 1H, 13C and IR spectrometry and elemental analysis. By means of thermodynamic and kinetic measurements we have also assessed the value of the equilibrium constant of the olefin exchange reaction between the naphthoquinone derivative 2d and the olefins ma, fn and tmetc. The coordinative ability of the studied olefins was confirmed and ranked in the general reactivity scale published so far. 4. Experimental 4.1. Solvents and reagents CH2Cl2 was distilled over CaH2 under inert atmosphere (Ar). Acetone was dried by means of molecular sieves (A4) and all the other chemicals were commercially available grade products unless otherwise stated. The IR, 1H, 13C and 31P NMR spectra were recorded on a Perkin-ElmerÒ Spectrum One spectrophotometer and on a BrukerÒ 300 Avance spectrometer, respectively. UV–Vis spectra were obtained on a Perkin-ElmerÒ k 40 UV–Vis spectrophotometer. Chemical shifts (ppm) are given related to TMS (1H and 13C NMR). Peaks are labelled as singlet (s), doublet (d), triplet (t), quartet (q), multiplet (m) and broad (b). The proton and carbon assignments were carried out by 1H-2D COSY, 1H-2D NOESY, 1 H–13C HMQC and HMBC experiments. IR spectra were recorded on a Perkin-Elmer Spectrum One spectrophotometer. The full characterization is reported only for the new complexes. 4.2. Spectrophotometric studies 4.2.1. Determination of the equilibrium constants by direct titration To 50 ml of a solution of the complex 2d in CHCl3 ([2d] = 1  104 mol dm3), microaliquots of a concentrated solution of the titrant olefins ol2 (ol2 = ma, fn; [ol2] = 1  102 mol dm3) were added at 298 K. The ensuing spectra were recorded in the wavelength interval 300–600 nm. The absorbance values at

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401.4 nm (highest absorbance changes) were treated by means of the locally adapted SCIENTISTÒ subroutine:

KE ¼ ð½Pdðg2 -ol2 ÞðL—L0 Þ½nqÞ=ð½Pdðg2 -nqÞðL—L0 Þ½ol2 Þ ½Pd0 ¼ ½Pdðg2 -ol2 ÞðL—L0  þ ½Pdðg2 -nqÞðL—L0 Þ ½ol2 0 ¼ ½ol2  þ ½Pdðg2 -ol2 ÞðL—L0  ½nq0 ¼ ½nq þ ½Pdðg2 -nqÞðL—L0 Þ Abs ¼ e½Pdðg2 -nqÞðL—L0 Þ ½Pdðg2 -nqÞðL—L0 Þ þ ðe½Pdðg2 -ol2 ÞðL—L0 Þ þ enq Þ  ½Pdðg2 -ol2 ÞðL—L0 Þ 4.2.2. Determination of the equilibrium constants from kinetic data To 3 ml of a solution of the complex 2d or 2a ([2] = 1  104 mol dm3) in the thermostatted cell compartment of a P.E. k 40 spectrophotometer, variable amounts of a mother solution of the olefin tmetc or nq ([ol] = 0.1 mol dm3) were added, respectively. The absorbance change versus time data recorded for each measure were treated by non linear regression analysis in the ORIGINÒ computing environment. The kobs obtained were analyzed by linear regression of the kobs data versus the concentration of the entering olefin. The slopes of the straight lines represent the kf or the kr of the equilibrium: 2d + tmetc = 2a + nq. 4.3. Synthesis of the type 2 complexes The imidazolium salt (1-methyl-3-((6-methylpyridine-2yl)methyl)-imidazol-3-ium) bromide (Me–NHC–CH2–PyHBr) and its chloride derivative (Me–NHC–CH2–PyHCl) were prepared according to Refs. [7] and [8], respectively. Type 1 complexes were synthesized according to Ref. [9]. Type 2 complexes were synthesized according to Ref. [7b]. The characterization data for the new complex 2b are reported below. Complex 2b: Yield 85%. White microcrystals. 1 H NMR (CD2Cl2, T = 298 K, ppm) d: 2.41 (bd, 1H, CH@CH), 3.16 (bd, 1H, CH@CH), 3.87 (s, 3H, NCH3), 5.10, 5.26 (AB system, J = 14.7 Hz, 2H, NCH2), 6.98 (d, J = 1.8 Hz, 1H, CH@CH Im), 7.10 (d, J = 1.8 Hz, 1H, CH@CH Im), 7.43 (ddd, J = 7.7, 5.3, 0.7 Hz, 1H, 5Pyr), 7.54 (d, J = 7.7 Hz, 1H, 3-Pyr), 7.89 (td, J = 7.7, 1.7 Hz, 1H, 4Pyr), 9.08 (ddd, J = 5.3, 1.7, 0.8 Hz, 1H, 6-Pyr). 13 C{1H} NMR (CDCl3, T = 298 K, ppm) d: 15.2 (CH, CH@CH), 17.7 (CH, CH@CH), 38.3 (CH3, NCH3), 55.3 (CH2, NCH2), 120.6 (CH, CH@CH Im), 120.7 (CH, CH@CH Im), 121.2 (C, NC); 124.4 (CH, 3Pyr), 124.6 (CH, 5-Pyr), 125.1 (C, NC); 138.3 (CH, 4-Pyr), 153.4 (C, 2-Pyr), 154.4 (CH, 6-Pyr), 187.7 (C, NCN). IR (KBr pellet) mCN: 2190 cm1. Anal. Calc. for C14H13N5Pd: C, 47.01; H, 3.66; N, 19.58. Found: C, 47.28; H, 3.71; N, 19.42%. 4.4. Synthesis of the type 3 complexes Complex 3a: To 60 mg (0.111 mmol) of the complex 2a dissolved in 15 ml of anhydrous CH2Cl2 under inert atmosphere (Ar), 30 mg (0.114 mmol) of PPh3 were added dropwise. The resulting pale yellow solution was stirred for 15 min and then dried under vacuum. The residual was suspended in diethyl ether stirred for some minutes, filtered off on a gooch and dried under vacuum. 83.1 mg of the title complex were obtained as pale-yellow microcrystals (yield 93%). 1 H NMR (CDCl3, T = 298 K, ppm) d: 3.24 (s, 3H, OCH3), 3.29 (s, 3H, OCH3), 3.51 (s, 3H, OCH3), 3.52 (s, 3H, OCH3), 3.67 (s, 3H, NCH3), 5.19, 5.17 (AB system, J = 14.7 Hz, 2H, NCH2), 6.64 (d,

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J = 1.8 Hz, 1H, CH@CH Im), 7.04–7.35 (m, 19H, CH@CH Im, 5-Pyr, 3Pyr, 4-Pyr, PPh), 8.48 (m, 1H, 6-Pyr). 13 C{1H} NMR (CDCl3, T = 243 K, ppm) d: 37.1 (CH3, NCH3), 51.4 (CH3, OCH3), 52.1 (CH3, OCH3), 52.5 (CH3, OCH3), 52.6 (CH3, OCH3), 55.8 (CH2, NCH2), 60.8 (C, C@C trans-C), 61.4 (d, JCP = 38.7 Hz, C, C@C trans-P), 121.8 (CH, CH@CH Im), 121.9 (CH, CH@CH Im), 123.0 (CH, 5-Pyr), 124.6 (CH, 3-Pyr), 137.1 (CH, 4-Pyr), 149.1 (CH, 6-Pyr), 155.7 (C, 2-Pyr), 169.9 (C, C@O), 170.7 (d, JCP = 5.5 Hz, C, C@O), 171.0 (d, JCP = 3.5 Hz, C, C@O), 171.3 (C, C@O), 187.7 (d, JCP = 17.0 Hz, C, NCN). 31 1 P{ H} NMR (CDCl3, T = 298 K, ppm) d: 28.9 (s, PPh3). IR (KBr pellet) mCO: 1672, 1711 cm1. Anal. Calc. for C38H38N3O8PPd: C, 56.90; H, 4.78; N, 5.24. Found: C, 57.17; H, 4.61; N, 5.03%. The following complexes were obtained by the same procedure as complex 3a by reacting PPh3 with the appropriate type 2 complexes. Complex 3b: Yield 85%. Whitish microcrystals. 1 H NMR (CD2Cl2, T = 298 K, ppm) d: 2.64–2.74 (m, 2H, CH@CH), 3.37 (s, 3H, NCH3), 4.96, 5.05 (AB system, J = 14.7 Hz, 2H, NCH2), 6.87 (d, J = 1.8 Hz, 1H, CH@CH Im), 7.06 (d, J = 7.8 Hz, 1H, 3-Pyr), 7.10 (d, J = 1.8 Hz, 1H, CH@CH Im), 7.11 (m partially overlapped, 1H, 5-Pyr), 7.04–7.45 (m, 16H, 4-Pyr, PPh), 8.47 (d, J = 5.1 Hz,1H, 6-Pyr). 13 C{1H} NMR (CDCl3, T = 298 K, ppm) d: 21.0 (d, J = 3 Hz, CH, C@C trans-C), 21.8 (d, JCP = 40.4 Hz, C, C@C trans-P), 37.2 (CH3, NCH3), 55.8 (CH2, NCH2), 121.8 (CH, CH@CH Im), 122.0 (CH, CH@CH Im), 122.8 (CH, 5-Pyr), 123.0 (CH, 3-Pyr), 123.8 (d, JCP = 2.5 Hz, C, NC), 124.8 (d, JCP = 8.0 Hz, C, NC), 136.9 (CH, 4Pyr), 149.3 (CH, 6-Pyr), 155.6 (C, 2-Pyr), 189.0 (d, JCP = 12.5 Hz, C, NCN). 31 1 P{ H} NMR (CDCl3, T = 298 K, ppm) d: 29.0 (s, PPh3). (See Fig. S12). IR (KBr pellet) mCN: 2190 cm1. Anal. Calc. for C32H28N5PPd: C, 61.99; H, 4.55; N, 11.30. Found: C, 61.78; H, 4.73; N, 11.07;%. Complex 3c: Yield 97%. Whitish microcrystals. 1 H NMR (CD2Cl2, T = 298 K, ppm) d: 3.29 (s, 3H, NCH3), 3.73 (dd, J = 3.8, 2.5 Hz, 1H, CH@CH trans-C), 3.96 (bd, 1H, CH@CH trans-P), 4.83, 4.97 (AB system, J = 14.9 Hz, 2H, NCH2), 6.84 (d, J = 1.8 Hz, 1H, CH@CH Im), 7.00 (d, J = 7.8 Hz, 1H, 3-Pyr), 7.05 (d, J = 1.8 Hz, 1H, CH@CH Im), 7.11 (dd, J = 7.8, 5.6 Hz, 1H, 5-Pyr), 7.18–7.44 (m, 16H, 4-Pyr, PPh), 8.46 (d, J = 5.6 Hz, 1H, 6-Pyr). 13 C{1H} NMR (CDCl3, T = 298 K, ppm) d: 37.3 (CH3, NCH3), 44.8 (CH, HC@CH trans-C), 46.8 (d, JCP = 29.4 Hz, CH, HC@CH trans-P), 55.8 (CH2, NCH2), 121.8 (CH, CH@CH Im), 122.1 (CH, CH@CH Im), 122.8 (CH, 5-Pyr), 122.9 (CH, 3-Pyr), 136.9 (CH, 4-Pyr), 149.1 (CH, 6-Pyr), 155.6 (C, 2-Pyr), 188.6 (d, JCP = 18.0 Hz, C, NCN). 31 1 P{ H} NMR (CDCl3, T = 298 K, ppm) d: 33.3 (bs, PPh3). IR (KBr pellet) mCO: 1714, 1785 cm1. Anal. Calc. for C32H28N3O3PPd: C, 60.06; H, 4.41; N, 6.57. Found: C, 59.81; H, 4.65; N, 6.33%. Complex 3d: Yield 86%. Orange microcrystals. 1 H NMR (CD2Cl2, T = 233 K, ppm). Selected signals of isomer A (55%). d: 2.84 (s, 3H, NCH3), 4.41 (d, J = 15.0, 1H, NCH2), 4.54–4.64 (m, partially overlapped, 2H, CH@CH, trans-C and trans-P), 5.00 (d, J = 15.0, 1H, NCH2), 6.75 (d, J = 1.8 Hz, 1H, CH@CH Im), 6.91 (d, J = 1.8 Hz, 1H, CH@CH Im), 7.78 (d, J = 7.7 Hz, 1H, 3-Pyr), 8.50 (d, J = 4.9 Hz,1H, 6-Pyr). Selected signals of isomer B (45%). d: 3.02 (s, 3H, NCH3), 4.36 (d, J = 15.0, 1H, NCH2), 4.54–4.64 (m, partially overlapped, 1H, CH@CH, trans-C), 4.76 (d, J = 15.0, 1H, NCH2), 5.03 (dd, J = 9.9, 7.2 Hz, 1H, CH@CH, trans-P), 6.70 (d, J = 1.8 Hz, 1H, CH@CH Im), 6.86 (d, J = 1.8 Hz, 1H, CH@CH Im), 6.01 (d, J = 7.5 Hz, 1H, 3-Pyr), 8.33 (d, J = 4.8 Hz, 1H, 6-Pyr). 13 C{1H} NMR (CD2Cl2, T = 233 K, ppm).

Selected signals of isomer A (55%). d: 36.9 (CH3, NCH3), 55.7 (CH2, NCH2), 63.4 (CH, C@C trans-C), 65.5 (d, JCP = 18.1 Hz, C, C@C trans-P), 122.2 (CH, CH@CH Im), 122.9 (CH, CH@CH Im), 124.8 (CH, 3-Pyr), 124.9 (CH, 5-Pyr), 137.2 (CH, 4-Pyr), 149.2 (CH, 6Pyr), 156.0 (C, 2-Pyr), 182.5 (d, JCP = 7.0 Hz, C, CO trans-P), 182.8 (C, CO trans-C), 187.3 (d, JCP = 7.0 Hz, C, NCN). Selected signals of isomer B (45%). d: 37.4 (CH3, NCH3), 55.2 (CH2, NCH2), 63.7 (CH, C@C trans-C), 65.1 (d, JCP = 18.8 Hz, C, C@C trans-P), 121.4 (CH, CH@CH Im), 122.1 (CH, 3-Pyr), 122.7 (CH, 5Pyr), 123.0 (CH, CH@CH Im), 136.7 (CH, 4-Pyr), 148.9 (CH, 6-Pyr), 155.3 (C, 2-Pyr), 183.1 (d, JCP = 6.8 Hz, C, CO trans-P), 183.6 (C, CO trans-C), 187.0 (d, JCP = 7.4 Hz, C, NCN). 31 1 P{ H} NMR (CDCl3, T = 298 K, ppm) Isomer A d: 34.4 (bs, PPh3); isomer Bd: 32.0 (bs, PPh3). IR (KBr pellet) mCO: 1586, 1616 cm1. Anal. Calc. for C38H32N3O2PPd: C, 65.19; H, 4.61; N, 6.00. Found: C, 65.37; H, 4.72; N, 5.81%. 4.5. Synthesis of the type 4 complexes The following complexes were obtained by the same procedure as complex 3a by reacting the DIC isocyanide with the appropriate type 2 complexes. The dried complexes were recovered and washed with the solvents indicated in parenthesis. Complex 4a: Yield 82%. Whitish microcrystals (hexane). 1 H NMR (CD2Cl2, T = 298 K, ppm) d: 2.18 (s, 6H, PhCH3), 3.63 (s, 6H, OCH3), 3.71 (s, 6H, OCH3), 3.81 (s, 3H, NCH3), 5.44 (s, 2H, NCH2), 6.94 (d, J = 1.8 Hz, 1H, CH@CH Im), 7.04 (d, J = 21 7.9 Hz, 2H, m-Ph), 7.15 (t, J = 7.9 Hz, 2H, p-Ph), 7.16 (d, J = 1.8 Hz, 1H, CH@CH Im), 7.49–7.52 (m, 2H, 3-Pyr, 4-Pyr), 8.43 (d, J = 4.8 Hz, 1H, 6-Pyr). IR (KBr pellet) mCO: 1680, 1702, 1738; mCN: 2142 cm1. Anal. Calc. for C29H32N4O8Pd: C, 51.91; H, 4.81; N, 8.35. Found: C, 52.18; H, 4.98; N, 8.04%. Complex 4b: Yield 86%. Whitish microcrystals (hexane). 1 H NMR (CDCl3, T = 298 K, ppm) d: 2.32 (s, 6H, PhCH3), 2.60 (d, J = 9.3 Hz, 1H HC@CH), 2.89 (d, J = 9.3 Hz, 1H, HC@CH), 3.87 (s, 3H, NCH3), 5.50, 5.38 (AB system, J = 15.0 Hz, 2H, NCH2), 7.02 (d, J = 1.8 Hz, 1H, CH@CH Im), 7.10 (d, J = 7.5 Hz, 2H, m-Ph), 7.15 (t, J = 7.9 Hz, 2H, p-Ph), 7.18 (d, J = 1.8 Hz, 1H, CH@CH Im), 7.11 (m partially overlapped, 1H, 5-Pyr), 7.32 (d, J = 7.8 Hz, 1H, 3-Pyr), 7.63 (td, J = 7.8, 1.8 Hz, 1H, 4-Pyr), 8.53 (d, J = 4.8 Hz, 1H, 6-Pyr). 13 C{1H} NMR (CDCl3, T = 298 K, ppm) d: 18.7 (CH3, PhCH3), 19.2 (CH, CH@CH), 20.3 (CH, CH@CH), 38.1 (CH3, NCH3), 56.3 (CH2, NCH2), 121.9 (CH, 5-Pyr), 122.3 (CH, CH@CH Im), 122.6 (CH, CH@CH Im), 122.8 (CH, 3-Pyr), 123.6 (C, NC), 123.8 (C, NC), 136.9 (CH, 4-Pyr), 149.5 (CH, 6-Pyr), 156.1 (C, 2-Pyr), 187.3 (C, NCN). IR (KBr pellet) mCN: 2123, 2197 cm1. Anal. Calc. for C23H22N6Pd: C, 56.51; H, 4.54; N, 17.19. Found: C, 56.63; H, 4.42; N, 17.27%. Complex 4c: Yield 93%. Yellow microcrystals (diethyl ether/hexane, pentane). 1 H NMR (CDCl3, T = 298 K, ppm) d: 2.31 (bs, 6H, PhCH3), 3.80 (s, 3H, NCH3), 3.82 (d, J = 3.9 Hz, 1H HC@CH), 4.03 (d, J = 3.9 Hz, 1H, HC@CH), 5.41, 5.35 (AB system, J = 15.2 Hz, 2H, NCH2), 7.00 (d, J = 1.8 Hz, 1H, CH@CH Im), 7.09 (d, J = 7.9 Hz, 2H, m-Ph), 7.13 (d, J = 1.8 Hz, 1H, CH@CH Im), 7.12–7.25 (m 3H, 5-Pyr, 3-Pyr, p-Ph), 7.61 (td, J = 7.7, 1.7 Hz, 1H, 4-Pyr), 8.50 (d, J = 4.8 Hz, 1H, 6-Pyr). IR (KBr pellet) mCO: 1714, 1794; mCN: 2140 cm1. Anal. Calc. for C23H22N4O3Pd: C, 54.29; H, 4.36; N, 11.01. Found: C, 54.11; H, 4.43; N, 10.87%. 4.6. Synthesis of the type 5 complexes Complex 5a was synthesized as complex 3a. Complex 5a: Yield 65%. Yellowish microcrystals.

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H NMR (CD2Cl2, T = 298 K, ppm) d: 1.14 (t, J = 7.0 Hz, 9H, POCH2CH3), 3.51 (s, 6H, OCH3), 3.60 (s, 6H, OCH3), 3.72 (s, 3H, NCH3), 3.84 (m, 6H, POCH2CH3), 5.37 (bs, 2H, NCH2), 7.03 (d, J = 1.8 Hz, 1H, CH@CH Im), 7.09 (d, J = 1.8 Hz, 1H, CH@CH Im), 7.20–7.26 (m, 2H, 5-Pyr, 3-Pyr), 7.66 (td, J = 7.7, 1.8 Hz, 1H, 4Pyr), 8.57 (m, 1H, 6-Pyr). 13 C{1H} NMR (CD2Cl2, T = 243 K, ppm) d: 16.3 (d, JCP = 6.8 Hz, CH3, POCH2CH3), 37.4 (CH3, NCH3), 51.9 (CH3, OCH3), 52.0 (CH3, OCH3), 55.6 (CH2, NCH2), 59.7 (d, JCP = 2.0 Hz, CH2, POCH2CH3) 60.3 (C, C@C trans-C), 60.6 (d, JCP = 35.4 Hz, C, C@C trans-P), 121.5 (CH, CH@CH Im), 122.2 (CH, 3-Pyr), 122.7 (CH, CH@CH Im), 122.7 (CH, 5-Pyr), 136.9 (CH, 4-Pyr), 149.2 (CH, 6-Pyr), 156.5 (C, 2-Pyr), 170.1 (C, C@O), 170.2 C, C@O), 184.5 (d, JCP = 32.7 Hz, C, NCN). 31 1 P{ H} NMR (CDCl3, T = 298 K, ppm) d: 144.4 (s, P(OEt)3). IR (KBr pellet) mCO: 1682, 1727 cm1. Anal. Calc. for C26H38N3O11PPd: C, 44.23; H, 5.43; N, 5.95. Found: C, 44.39; H, 5.55; N, 5.74%. Owing to the partial decomposition observed throughout the washing, the following complexes 5b and 5c, were prepared as the complexes described above but separated only by drying under vacuum of the crude product without further purification thus, no elemental analysis is reported in these cases. Complex 5b: Yield > 95%. Yellowish solid. 1 H NMR (CDCl3, T = 298 K, ppm) d: 1.24 (t, J = 7.0 Hz, 9H, POCH2CH3), 2.35 (dd, J = 13.5, 9.3 Hz, 1H, CH@CH trans-P), 2.77 (dd, J = 9.3, 4.5 Hz, 1H, CH@CH trans-C), 3.78 (s, 3H, NCH3), 3.88 (m, 6H, POCH2CH3), 5.28, 5.42 (AB system, J = 15.1 Hz, 2H, NCH2), 7.00 (d, J = 1.8 Hz, 1H, CH@CH Im), 7.15 (d, J = 1.8 Hz, 1H, CH@CH Im), 7.22–7.28 (m, 2H, 5-Pyr, 3-Pyr), 7.70 (td, J = 7.7, 1.8 Hz, 1H, 4-Pyr), 8.59 (d, J = 4.8 Hz, 1H, 6-Pyr). 31 1 P{ H} NMR (CDCl3, T = 298 K, ppm) d: 147.8 (s, P(OEt)3). Complex 5c Yield > 95%. Dark oil. 1 H NMR (CDCl3, T = 298 K, ppm) d: 1.21 (t, J = 7.0 Hz, 9H, POCH2CH3), 3.68 (dd, J = 11.3, 4.0 Hz, 1H, CH@CH trans-P), 3.71 (s, 3H, NCH3), 3.82–3.94 (m, 7H, CH@CH trans-C, POCH2CH3), 5.37, 5.22 (AB system, J = 15.3 Hz, 2H, NCH2), 6.97 (d, J = 1.8 Hz, 1H, CH@CH Im), 7.08 (d, J = 1.8 Hz, 1H, CH@CH Im), 7.19 (d, J = 7.7 Hz 1H, 3Pyr), 7.19 (dd, J = 7.7, 4.3, Hz 1H, 3-Pyr), 7.68 (td, J = 7.7, 1.8 Hz, 1H, 4-Pyr), 8.57 (d, J = 4.3 Hz, 1H, 6-Pyr). 31 1 P{ H} NMR (CDCl3, T = 298 K, ppm) d: 147.8 (s, P(OEt)3). Appendix A. Supplementary material Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.ica.2014.06.017. References [1] (a) F. Diederich, P.J. Stang, in: F. Diederich, P.J. Stang (Eds.), Metal-Catalyzed Cross-Coupling Reactions, Wiley-VCH, Weinheim, 1998; (b) M.J. Calhorda, J.M. Brown, N.A. Cooley, Organometallics 10 (1991) 1431; (c) K. Selvakumar, M. Valentini, P.S. Pregosin, A. Albinati, Organometallics 18 (1999) 4591; (d) R.F. Heck, Acc. Chem. Res. 12 (1979) 146; (e)R.F. Heck, B.M. Trost, I. Fleming (Eds.), Comprehensive Organic Synthesis, 4, Oxford, Pergamon, 1991; (f) M.J. Brown, K.K. Hii, Angew. Chem. Int. Ed. Engl. 108 (1996) 679; (g) M. Tschoerner, P.S. Pregosin, A. Albinati, Organometallics 18 (1999) 670; (h) A. de Meijere, F.E. Meyer, Angew. Chem. Int. Ed. Engl. 106 (1994) 2473; (i) J.K. Stille, Angew. Chem. Int. Ed. Engl. 25 (1986) 508; (j) V. Farina, in: E.W. Abel, F.G.A. Stone, G. Wilkinson (Eds.), Comprehensive Organometallic Chemistry II, vol. 12, Pergamon, Oxford, 1995; (k) V. Farina, G.P. Roth, Adv. Metal Org. Chem. 5 (1996) 1; (l) B. Crociani, S. Antonaroli, L. Canovese, P. Uguagliati, F. Visentin, Eur. J. Inorg. Chem. (2004) 732; (m) A. Pfaltz, Acta Chem. Scand. 50 (1996) 189; (n) O. Reiser, Angew. Chem. Int. Ed. Engl. 105 (1993) 576. [2] (a) H. Hagelin, M. Svensson, B. Akermark, P.-O. Norby, Organometallics 18 (1999) 4574; (b) M.J.S. Dewar, Bull. Soc. Chim. Fr. 18 (1951) C71;

333

(c) J. Chatt, L.A. Duncanson, J. Chem. Soc. (1953) 2939; (d) P. Espinet, A.C. Albeniz, in: R. Crabtree, M. Mingos (Eds.), ‘‘Palladium– Carbon p Bonded Complexes’’ Comprehensive Organometallic Chemistry III, vol. 8, Elsevier, 2007; (e) R. Van Asselt, C.J. Elsevier, W.J.J. Smeets, A.L. Speck, Inorg. Chem. 33 (1994) 1521; (f) P.T. Cheng, C.D. Cook, S.C. Nyburg, K.Y. Wan, Inorg. Chem. 10 (1971) 2210; (g) F. Ozawa, T. Ito, Y. Nakamura, A. Yamamoto, J. Organomet. Chem. 168 (1979) 375; (h) R. Van Asselt, C.J. Elsevier, Tetrahedron 50 (1994) 323; (i) F. Gomez-de la Torre, F.A. Jalon, A. Lopez-Agenjo, B.R. Manzano, A. Rodriguez, T. Sturm, W. Weissensteiner, M. Martinez-Ripoll, Organometallics 17 (1998) 4634; (j) S. Antonaroli, B. Crociani, J. Organomet. Chem. 560 (1998) 137; (k) M. Tschoerner, G. Trabesinger, A. Albinati, P.S. Pregosin, Organometallics 16 (1997) 3447; (l) J.-Y. Lee, P.-Y. Cheng, Y.-H. Tsai, G.-R. Lin, S.-O. Lin, M.-H. Sie, H.M. Lee, Organometallics 29 (2010) 3901; (m) S.N. Sluiter, S. Warsink, M. Lutz, C.J. Elsevier, Dalton Trans. 42 (2013) 7365; (n) P. Hauwert, J.J. Dunsford, D.S. Tromp, J.J. Weigand, M. Lutz, K.J. Cavell, C.J. Elsevier, Organometallics 32 (2013) 131. [3] (a) A. Bader, E. Lindner, Coord. Chem. Rev. 108 (1991) 27; (b) C.S. Slone, D.A. Weinberger, C.A. Mirkin, Prog. Inorg. Chem. 48 (1999) 233– 350; (c) S.W. Kohl, L. Weiner, L. Schwartsburd, L. Konstantinovski, L.J.W. Shimon, Y. Ben-David, M.A. Iron, D. Milstein, Science 324 (2009) 74; (d) M. Feller, E. Ben-Ari, M.A. Iron, Y. Diskin-Posner, G. Leitus, L.J.W. Shimon, L. Konstantinovski, D. Milstein, Inorg. Chem. 49 (2010) 1615; (e) J.L. van der Vlugt, E.A. Pidko, D. Vogt, M. Lutz, A.L. Spek, Inorg. Chem. 48 (2009) 7513; (f) J.I. van der Vlugt, M.A. Siegler, M. Janssen, D. Vogt, A.L. Spek, Organometallics 28 (2009) 7025; (g) R. Lindner, B. van der Bosch, M. Lutz, J.N.H. Reek, J.I. van der Vlugt, Organometallics 30 (2011) 499; (h) M.T. Whited, R.H. Grubbs, Acc. Chem. Res. 42 (2009) 1607; M. Gagliardo, N. Selander, N.C. Mehendale, G. van Koten, R.J.M. Klein Gebbink, K.J. Szabó, Chem. Eur. J. 14 (2008) 4800; I. Moreno, R. San Martin, B. Inés, M.T. Herrero, E. Dominguez, Curr. Org. Chem. 13 (2009) 878; (k) D.M. Spasyuk, D. Zargarian, A. van der Est, Organometallics 28 (2009) 6531; S. Bonnet, J. Li, M.A. Siegler, L.S. von Chrzanowski, A.L. Spek, G. van Koten, R.J.M. Klein Gebbink, Chem. Eur. J. 15 (2009) 3340; (m) V.A. Kozlov, D.V. Aleksanyan, Y.V. Nelyubina, K.A. Lyssenko, A.A. Vasil’ev, P.V. Petrovski, I.L. Odinets, Organometallics 29 (2010) 2054; (n) D.M. Spasyuk, D. Zargarian, Inorg. Chem. 49 (2010) 6203; (o) J.-L. Niu, Q.-T. Chen, X.-Q. Hao, Q.-X. Zhao, J.-F. Gong, M.-P. Song, Organometallics 29 (2010) 2248; (p) B.-S. Zang, W. Wang, D.D. Shao, X.-D. Hao, J.-F. Gong, M.-P. Song, Organometallics 29 (2010) 2579; (q) M.A. Siegler, M. Lutz, A.L. Spek, R.J.M. Klein Gebbink, G. van Koten, Adv. Synth. Catal. 352 (2010) 2474; (r) S. Warsink, C.M.S. van Aubel, J.J. Weigand, S.-T. Liu, C.J. Elsevier, Eur. J. Inorg. Chem. (2010) 5556; (s) S. Warsink, J.-H. Chang, J.J. Weigand, P. Hauwert, J.-J. Chen, C.J. Elsevier, Organometallics 29 (2010) 4555. [4] (a) J.C. Jeffrey, T.B. Rauchfuss, Inorg. Chem. 18 (1979) 2658; (b) P. Braunstein, F. Naud, Angew. Chem. Int. Ed. 40 (2001) 680. [5] (a) H.M. Lee, C.-C. Lee, P.-Y. Cheng, Curr. Org. Chem. 11 (2007) 1491; (b) A.T. Normand, K.J. Cavell, Eur. J. Inorg. Chem. (2008) 2781; (c) M.C. Jahnke, T. Pape, F.E. Hahn, Eur. J. Inorg. Chem. (2009) 1960; (d) D. Meyer, M.A. Taige, A. Zeller, K. Hohlfeld, S. Ahrens, T. Strassner, Organometallics 28 (2009) 2142; (e) A.R. Chianese, P.T. Bremer, C. Wong, R.J. Reynes, Organometallics 28 (2009) 5244; (f) W.W.N.O., A.J. Lough, R.H. Morris, Organometallics 28 (2009) 6755; (g) S. Warsink, P. Hauwert, M.A. Siegler, A.L. Spek, C.J. Elsevier, Appl. Organomet. Chem. 23 (2009) 225; (h) S. Warsink, S.Y.D. Boer, L.M. Jongens, C.-F. Fu, S.-T. Liu, J.-T. Chen, M. Lutz, A.L. Spek, C.J. Elsevier, Dalton Trans. (2009) 7080; (i) C. Lu, S. Gu, W. Chen, H. Qiu, Dalton Trans. 39 (2010) 4198; (j) S. Warsink, R.M. Drost, M. Lutz, A.L. Spek, C.J. Elsevier, Organometallics 29 (2010) 3109; (k) D.S. Mc Guiness, K.J. Cavell, Organometallics 19 (2000) 741; (l) A.A.D. Tulloch, A.A. Danopoulos, S. Kleinhenz, M.E. Light, M.B. Hursthouse, G. Eastham, Organometallics 20 (2001) 2027; (m) S. Winston, N. Stylianides, A.A.D. Tulloch, J.A. Wright, A.A. Danopoulos, Polyhedron 23 (2004) 2813; (n) X. Wang, S. Liu, G.-X. Jin, Organometallics 23 (2004) 6002; (o) M. Yigit, B. Yigit, I. Ozdemir, E. Cetinkaya, B. Cetinkaya, Appl. Organomet. Chem. 20 (2006) 322; (p) F. Zeng, Z. Yu, J. Org. Chem. 71 (2006) 5274; (q) L. Mercs, G. Labat, A. Neels, A. Ehlers, M. Albrecht, Organometallics 25 (2006) 5648; (r) Z. Xi, X. Zhang, W. Chen, S. Fu, D. Wang, Organometallics 27 (2007) 6636; (s) Z. Xi, B. Liu, W. Chen, J. Org. Chem. 73 (2008) 3954; (t) X. Zhang, Z. Xi, A. Liu, W. Chen, Organometallics 27 (2008) 4401;

334

[6] [7]

[8]

[9]

L. Canovese et al. / Inorganica Chimica Acta 421 (2014) 326–334 (u) X. Zhang, B. Liu, A. Liu, W. Xie, W. Chen, Organometallics 28 (2009) 1336; (v) Z. Xi, B. Liu, V. Lu, W. Chen, Dalton Trans. (2009) 7008; (w) B. Liu, A. Liu, Y. Zhou, W. Chen, Organometallics 29 (2010) 1457; (x) P.L. Chiu, C.-L. Lai, C.-F. Chang, C.-H. Hu, H.M. Lee, Organometallics 24 (2005) 6169; (y) M.C. Jahnke, T. Pape, F.E. Hahn, Eur. J. Inorg. Chem. (2009) 1960. L. Canovese, F. Visentin, C. Levi, A. Dolmella, Dalton Trans. 40 (2011) 966. (a) L.R. Titcomb, S. Caddick, F.G.N. Cloke, D.J. Wilson, D. Mc, Chem. Commun. (2001) 1388; (b) S. Fantasia, S.P. Nolan, Chem. Eur. J. (2008) 6987. (a) A.A.D. Tulloch, A.A. Danopoulos, S. Winston, S. Kleinhenz, G. Eastham, J. Chem. Soc., Dalton Trans. (2000) 4499; (b) L. Canovese, F. Visentin, C. Levi, C. Santo, V. Bertolasi, Inorg. Chim. Acta 390 (2012) 105. S. Warsink, S.Y.D. Boer, L.M. Jongens, C.-F. Fu, S.-T. Liu, J.-T. Chen, M. Lutz, A.L. Spek, C.J. Elsevier, Dalton Trans. (2009) 7080.

[10] L. Canovese, F. Visentin, G. Chessa, P. Uguagliati, C. Levi, A. Dolmella, Organometallics 24 (2005) 5537. [11] L. Canovese, F. Visentin, G. Chessa, P. Uguagliati, A. Dolmella, J. Organomet. Chem. 601 (2000) 1. [12] (a) L. Canovese, F. Visentin, C. Santo, V. Bertolasi, J. Organomet. Chem. 749 (2014) 379; (b) L. Canovese, F. Visentin, C. Levi, C. Santo, V. Bertolasi, Inorg. Chim. Acta 378 (2011) 239; (c) L. Canovese, F. Visentin, C. Santo, A. Dolmella, J. Organomet. Chem. 694 (2009) 411. [13] L. Canovese, F. Visentin, Inorg. Chim. Acta 363 (2010) 2375. [14] L. Canovese, F. Visentin, G. Chessa, P. Uguagliati, G. Bandoli, Organometallics 19 (2000) 1461. [15] M. Frøset, K.A. Netland, K.W. Törnroos, A. Dhindsa, M. Tilset, Dalton Trans. (2005) 1664.