New palladium(II) complexes with bis(pyrazol-1-yl)alkanes

www.elsevier.nl/locate/ica Inorganica Chimica Acta 295 (1999) 136 – 145

New palladium(II) complexes with bis(pyrazol-1-yl)alkanes Gregorio Sa´nchez a, Jose´ L. Serrano a, Jose´ Pe´rez a, M. Carmen Ramı´rez de Arellano a, Gregorio Lo´pez a,*, Elies Molins b b

a Departamento de Quı´mica Inorga´nica, Uni6ersidad de Murcia, E-30071 Murcia, Spain Institut de Cie`ncia de Materials de Barcelona, CSIC, Campus Uni6ersitari de Bellaterra, E-08193 Bellaterra, Barcelona, Spain

Received 30 April 1999; accepted 2 July 1999

Abstract The replacement of chloride ligands in [Pd(NN)Cl2] (NN= bpzm: bis(pyrazol-1-yl)methane, bpzm*: bis(3,5-dimethylpyrazol1-yl)methane) by a weak donor ligand such as acetonitrile has been achieved by treating the dichloro complexes with AgClO4 in this solvent. The reactivity of the new precursors [Pd(NN)(CH3CN)2][ClO4]2 towards a variety of neutral N- and P-donor ligands L (pyridine, triphenylphosphine, triethylphosphine) or L2 (1,2-bis(diphenylphosphino) ethane, ethylenediamine, N,N,N%,N%-tetramethylethylenediamine, 2,2%-bipyridine, o-phenylenediamine) has been studied. When chloride abstraction from [Pd(NN)Cl2] is carried out in Me2CO/H2O, the cationic hydroxo-bridged dimeric complexes [(NN)Pd(m-OH)2Pd(NN)]2 + are isolated as their perchlorate salts. The hydroxo complexes react with the protic electrophiles H(LL) (acetylacetone, salicylaldehyde and 2-pyrrol carbaldehyde) in a 1:2 molar ratio to give the corresponding mononuclear complexes [Pd(NN)(LL)][ClO4]. The 13C and 1H NMR assignments have been made on the basis of NOE studies and 1H – 1H COSY and 1H – 13C HETCOR experiments. The structures of [Pd(bpzm)(tmeda)][ClO4]2 and [Pd(bpzm*)(sal)][ClO4] have been determined by single-crystal X-ray diffraction studies; in both complexes the bis(pirazolyl)alkanes act as chelating ligands with coordination around the palladium atom slightly distorted from the square-planar geometry. © 1999 Elsevier Science S.A. All rights reserved. Keywords: Palladium complexes; Pyrazolylalkane complexes; Crystal structures

1. Introduction Although the chemistry of metal poly(pyrazol-1yl)borato complexes has been studied extensively [1], comparable development of the isoelectronic but neutral poly(pyrazol-1-yl)alkanes has received little attention [2]. Most of the published material concerns first-row transition metals [3] and some ruthenium(II) examples [4], while coordination to metals having the d8 configuration is rare and basically includes complexes of rhodium(I) [5] and some derivatives of dimethylgold(III) [6] and methyl or dimethylplatinum(II) [7] with tris(pyrazol-1-yl)alkanes. The interaction of the bis(pyrazol-1-yl)alkanes with palladium(II) is still largely unexplored [8–10], and only a few cationic allylic complexes have been reported recently [11]. On the other hand, it is well known that metal complexes containing weak donor ligands such as ace* Corresponding author.

tonitrile, alcohols, acetone or ethers are convenient precursors for the preparation of new coordination and organometallic compounds, specially those of palladium(II) and platinum(II) [12]. Complexes such as [M(C6F5)2(solvent)2] (M = Ni, Pd or Pt; solvent =dioxane [13], tetrahydrofuran [14–16] or benzonitrile [17– 19]) have been used as starting materials for the preparation of other organometallic compounds. The feasibility of the substitution process comes from the easy replacement of solvent molecules in the coordination sphere of the metal atom. Unfortunately, together with the high lability of such complexes, difficulties in isolating and characterizing them arise. Another subject which has received a growing interest in the last few years is the synthesis of hydroxo complexes of nickel group elements, owing to their reactivity and potential relevance to catalysis [20]. Their use as precursors in synthetic work is based on the considerable nucleophilicity of the bridging OH groups. Acid–base reactions of the type {M(m-OH)2M}+ 2H(LL) “

0020-1693/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved. PII: S 0 0 2 0 - 1 6 9 3 ( 9 9 ) 0 0 3 3 4 - 5

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2{M(LL)} or {M(m-LL)M} +2H2O may be used for the preparation of a wide variety of mono- or binuclear complexes [21–24] depending on the endo- or exo-bidentate nature of (LL)−. This paper deals with the synthesis of the cationic precursors [Pd(NN)(CH3CN)2]2 + and [Pd2(NN)2(mOH)2]2 + , NN being bis(pyrazol-1-yl)methane (bpzm) or bis(3,5-dimethylpyrazol-1-yl)methane (bpzm*). These complexes can be conveniently used for the preparation of new bis(pyrazol-1-yl)alkane derivatives of palladium(II), [Pd(NN)L2]2 + and [Pd(NN)(LL)]+, where L (or L2) is a neutral ligand and (LL)− an endo-bidentate anionic ligand, respectively. 2. Experimental

2.1. Physical measurements and materials The analyses (C, H, N) were performed with a Perkin– Elmer 240C microanalyser. IR spectra were recorded on a Perkin–Elmer 1430 spectrophotometer using Nujol mulls between polyethylene sheets. NMR data were recorded on a Bruker AC 200E (1H) or a Varian Unity 300 (13C, 31P) spectrometer. Conductance measurements were performed with a Crison 525 conductimeter (in acetone or dimethylsulfoxide solution; c:10 − 4 mol dm − 3). The precursors [Pd(NN)Cl2] (NN =bpzm, bpzm*) were prepared as described in the literature [8]. Table 1 Crystallographic data for complexes 8 and 23

Formula Molecular weight Crystal size (mm) Temperature (K) Crystal system Space group a (A, ) b (A, ) c (A, ) a (°) b (°) g (°) U (A, 3) Z Absorption coefficient (cm−1) Dcalc (g cm−3) Transmission factors 2u Range No. unique data No. observed data No. variables R R% Goodness-of-fit

8·H2O

23

C13H24Cl2N6O8Pd·H2O 587.70 0.74×0.20×0.16 173(2) orthorhombic P212121 10.962(3) 13.514(3) 14.300(3) 90.00(0) 90.00(0) 90.00(0) 2118.4(9) 4 11.9

C18H21ClN4O6Pd 531.24 0.40×0.30×0.20 293(2) triclinic P1( 8.205(2) 10.676(2) 13.365(3) 68.11(3) 89.53(3) 75.28(3) 1045.8(4) 2 10.6

1.843 0.75–0.90 6.01–50.02 3728 3581 290 0.0287 0.0302 1.063

1.687 0.97–1.00 5.74–60.88 6353 4106 272 0.0519 0.1396 1.028

Scheme 1.

The ligands bpzm [25] and bpzm* [26] were prepared according to reported procedures and all the solvents were dried by standard methods before use.

2.2. Preparation of the complexes 2.2.1. [Pd(NN)(CH3CN)2][ClO4]2 (NN= bpzm (1) or bpzm* (2)) AgClO4 was added to a suspension of [Pd(NN)Cl2] (0.1 g; molar ratio 2:1) in acetonitrile (10 cm3). The precipitation of AgCl commenced immediately. After 15 min of stirring at room temperature the precipitate was removed, and the resulting yellow solution concentrated under reduced pressure to half volume. Addition of diethyl ether caused the precipitation of the title complexes which were separated, washed with diethyl ether and air-dried. Complex 1: yield 70%. (Anal. Found: C, 24.5; H, 2.5; N, 15.5. Calc. for C11Cl2H14N6O8Pd: C, 24.6; H, 2.6; N, 15.4%). LM (S cm2 mol − 1) 253. IR (cm − 1) (Nujol): 2332, 2300, (CN str).

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Table 2 1 H and 13C NMR chemical shifts (d) and coupling constants (Hz) for complexes 3–24 Compd 1H a

(pseudo-t, 2H, H4,4%) (m, 4H, CH2+H3,3%) (m, 4H, py) (t, 2H, py, J34 = 7.1) (d, 2H, H5,5%, J54 = 2.9) (d, 4H, py, J23 = 5.2)

6.16 6.79 7.59 8.27

(pseudo-t, 2H, H4,4%) (s, 2H, CH2) (m, 32H, Ph+H3,3%) (d, 2H, H5,5%, J54 = 2.5)

5a

1.28 2.26 6.63 7.33 8.13 8.40

(m, 18H, CH3 of PEt3) (m, 12H, CH2 of PEt3) (pseudo-t, 2H, H4,4%) (s, 2H, CH2) (br, 2H, H3,3%) (d, 2H, H5,5%, J54 = 2.5)

6b

3.00 6.73 7.35 7.49 7.80 8.45

(m, 4H, CH2 of dppe) (pseudo t, 2H, H4,4%) (m, 16H, Ph+CH2 of bpzm) (m, 4H, Ph) (br, 2H, H3,3%) (d, 2H, H5,5%, J54 = l.9)

7a

2.93 4.75 6.26 6.40 7.46 7.86

(s, 4H, CH2 of en) (m, 4H, NH2) (pseudo-t, 2H, H4,4%) (s, 2H, CH2 of bpzm) (d, 2H, H3,3%, J54 = 2.0) (d, 2H, H5,5%, J54 = 2.4)

52.6 (CH2 of en) 64.0 (CH2 of bpzm) 110.1 (C4,4%) 137.2 (C5,5%) 144.4 (C3,3%)

2.92 3.21 3.30 6.66 7.33 7.92 8.22 8.42

(s, 6H, CH3 of tmeda) (s, 6H, CH3 of tmeda) (s, 4H, CH2 of tmeda) (pseudo-t, 2H, H4 4 ) (d, 1H CH2 of bpzm, JAB = 14.7) (d, 1H CH2 of bpzm, JAB = 14.7) (d, 2H, H3,3%, J34 = 2.3) (d, 2H, H5,5%, J54 = 2.7)

51.2 (CH3 of 52.5 (CH3 of 63.8 (CH2 of 64.2 (CH2 of 110.0 (C4,4%) 137.1 (C5,5%) 144.8 (C3,3%)

6.85 7.53 7.81 7.98 8.44 8.61 8.78

(pseudo-t, 2H, H4,4%) (d, 1H CH2 of bpzm, JAB = 14.4) (d, 1H CH2 of bpzm, JAB = 14.4) (m, 2H, H4,4% of bipy) (d, 2H, H3,3% J34 = 2.4) (m, 6H, H5,5%+H5,5%,6,6% of bipy) (d, 2H, H3,3% of bipy 1 = 7.6)

63.5 (CH2) 109.7 (C4,4%) 124.6 (C3,3% of 128.4 (C5,5% of 136.4 (C5,5%) 142.8 (C4,4% of 144.9 (C3,3%) 151.0 (C6,6% of 155.9 (C2,2% of

4a

8a

9a

10 b

11 a

6.76 6.99 7.39 8.12 8.37

(d, 1H, CH2 J =15.7) (m, 4H, py) (d, 1H, CH2 J =15.7) (t, 2H, py, J34 =7.6) (d, 4H, py, J23 =5.3)

12 b

1.96 2.52 3.00 6.29 6.92 7.35 7.52 7.75

(s, 6H, Me3,3%) (s, 6H, Me5,5%) (m, 4H, CH2 of dppe) (s, 4H, H4,4%) (d, 1H, CH2 of bpzm* J =15.5) (m, 12H, Ph) (m ,8H, Ph) (d, 1H, CH2 of bpzm* J =15.5)

13 a

2.07 2.66 2.95 4.79 6.30 7.06 7.85

(s, 6H, Me3,3%) (s, 6H, Me5,5%) (m, 4H, CH2 of en) (s, 4H, NH2) (s, 2H, H4,4%) (d, lH,CH2 of bpzm* J= 15.8) (d, lH,CH2 of bpzm* J= 15.8)

11.5 (Me5,5%) 13.8 (Me3,3%) 51.9 (CH2 of en) 59.3 (CH2 of bpzm*) 109.1 (C4,4%) 147.0 (C5,5%) 154.2 (C3,3%)

14 a

2.05 2.66 2.87 2.93 6.29 7.04 7.85

(s, 6H, Me3,3%) (s, 6H, Me5,5%) (s, 12H, Me of tmeda) (s, 4H, CH2 of Tmeda) (s, 2H, H4,4%) (d, 1H, CH2 of bpzm*, J =15.6) (d, 1H CH2 of bpzm*, J =15.6)

11.4 (Me5,5%) 13.6 (Me3,3%) 51.6 (Me of tmeda) 59.4 (CH2 of bpzm*) 64.7 (CH2Of tmeda) 109.9 (C4,4%) 146.9 (C5,5%) 154.4 (C3,3%)

15 a

2.50 (s, 6H, Me3,3%) 2.66 (s, 6H, Me5,5%) 6.40 (s, 2H, H4,4%) 7.08 (d, 1H, CH2 of bpzm*, J =15.6) 7.90 (m, 3H, CH2 of bpzm*+H6,6% bipy) 8.44 (d, 2H, H5,5% of bipy J54 =5.0) 8.55 (m, 2H, H4,4 of bipy) 8.73 (d, 2H, H3,3% of bipy J34 =8.1)

C{1H}

(pseudo t, 2H, H4,4%) (s, 2H, CH2) (m, 2H, opda) (m, 4H, H3,3%+2H of opda) (d, 2H, H5,5%, J54 = 2.3)

1.84 (s, 6H, Me3,3%) 2.62 (s, 6H,Me5,5%) 6.14 (s, 2H,Me4,4%)

64.3 (CH2) 109.3 (C4,4%) 128.6 (C3 of py) 137.0 (C5,5%) 142.4 (C4 of py) 144,3 (C3,3%) 153.0 (C2 of py)

tmeda) tmeda) tmeda) bpzm)

16 a

bipy) bipy) bipy) bipy) bipy)

63.1 (CH2) 108.5 (C4,4%) 126.3 (C3,6 of opda) 128.6 (C3,6 of opda) 135.9 (C5,5%) 139.3 (C1,2 of opda) 144.3 (C3,3%) 11.3 (Me5,5%) 13.6 (Me3,3%) 59.1 (CH2)

2.53 (s, 6H, Me3,3%) 2.58 (s, 6H, Me5,5%) 6.26 (s, 2H, H4,4%) 6.81 (d, 1H, CH2 of bpzm*, J =15.4) 7.30 (m, 4H, NH2) 7.39 (m, 3H, CH2 of bpzm*+2H opda) 7.51 (m, 2H, opda)

109.9 128.1 142.3 146.1 153.5 154.8

(C4,4%) (C3,5 of py) (C4 of py) (C5,5%) (C2,6 of py) (C3,3%)

6.99 7.75 7.97 8.19 9.44

13

6.58 7.44 7.82 8.24 8.42 9.43

3

Table 2 (Continued)

10.9 (Me5,5%) 14.2 (Me3,3%) 58.9 (CH2) 109.8 (C4,4%) 124.3 (C3,3% of bipy) 128.2 142.1 145.9 151.4 153.2 156.6

(C5,5% of (C4,4% of (C5,5%) (C6,6% of (C3,3%) (C2,2% of

bipy) bipy) bipy) bipy)

11.1 (Me5,5%) 13.6 (Me3,3%) 59.1 (CH2) 109.3 (C4,4%) 126.9 (C3,6 of opda) 129.5 (C4,5 of opda) 140.1 (C1,2 of opda) 145.8 (C5,5%) 154.5 (C3,3%)

17 b

6.74 7.28 7.82 8.46

(br, 4H, H4,4%) (s, 4H, CH2) (br, 4H, H3,3%) (s, 2H, H5,5%)

64.5 (CH2) 109.8 (C4,4%) 137.6 (C5,5%) 144.4 (C3,3%)

18 b

2.25 2.43 6.15 6.75 7.35

(s, 12H, Me3,3%) (s, 12H, Me5,5%) (s, 2H, H4,4%) (d, 1H, CH2 of bpzm*, J= 15.2) (d, 1H, CH2 of bpzm*, J= 15.6)

10.6 (Me5,5%) 12.3 (Me3,3%) 57.6 (CH2) 108.2 (C4,4%) 143.9 (C5,5%) 153.6 (C3,3%)

G. Sa´nchez et al. / Inorganica Chimica Acta 295 (1999) 136–145 Table 2 (Continued)

Table 2 (Continued)

Compd 1H

13

C{1H}

19 a

2.17 5.84 6.68 6.91 7.93 8.30

(s, 6H, Me of acac) (s, 1H, CH of acac) (s, 2H, H4,4%) (s, 2H, CH2 of bpzm) (s, 2H, H3,3%) (br, 2H, H5,5%)

25.3 (Me of acac) 63.7 (CH2) 102.6 (CH of acac) 108.8 (C4,4%) 136.8 (C5,5%) 143.1 (C3,3%) 188.5 (CO of acac)

20 a

6.84 6.87 7.14 7.67 7.81 8.09 8.15 8.41 8.87

(m, 2H, H4%+H6 of sal) (pseudo-t, 1H, H4) (br, 3H, CH2+H4 of sal) (m, 1H, H5 of sal) (d, 1H, H3 of sal, J =8.1) (d, 1H, H3%, J3%4% = 2.3) (d, 1H, H3, J34 = 2,3) (d, 2H, H5,5%, J54 = 2.7) (s, 1H, CHO of sal)

62.6 (CH2) 107.9 (C4%) 108.2 (C4) 117.5 (C6 of sal) 120.4 (C4 of sal) 122.3 (C2 of sal) 136.0 (C5%) 136.3 (C5%) 137.3 (C3 of sal) 140.8 (C5 of sal) 141.9 (C3%%) 142.3 (C3) 166.1 (C1 of sal) 191.4 (CO of sal)

21 a

6.44 6.71 6.78 7.22 7.38 8.04 8.20 8.24 8.40 8.48

(m, 1H, H4 of 2-pcal) (pseudo-t, 1H, H4%) (pseudo-t, 1H, H4) (s, 2H, CH2) (m, 2H, H3,5 of 2-pcal) (d, 1H, H3%, J3%4% = 1.8) (s, 1H, CHO of 2-pcal) d, 1H, H3, J34 = 2.3) (d, 1H, H5, J54 = 2.4) (d, 1H, H5, J54 = 2.7)

64.0 (CH2) 108.8 (C4%) 109.6 (C4) 116.7 (C4 of 2-pcal) 127.4 (C3 of 2-pcal) 136.1 (Cu5%) 137.1 (C5) 143.7 (C3%) 144.4 (C5 of 2-pcal) 145.0 (C2 of 2-pcal) 146.1 (C3) 183.6 (CO of 2-pcal)

22 a

2.12 2.45 2.58 5.82 6.21 6,84 7.25

(s, (s, (s, (s, (s, (s, (s,

11.1 (Me5,5%) 12.9 (Me3,3%) 24.8 (Me of acac) 58.8 (CH2 of bpzm*) 108.8 (CH of acac) 109.4 (C4,4%) 145.1 (C5,5%) 154.3 (C3,3%) 187.5 (CO of acac)

23 a

10.9 (Me5%) 2.49 (s, 3H, Me3%) 2.54 (s, 3H,Me3) 11.0 (Me5) 2.59 (s, 6H, Me5,5%) 12.7 (Me3%) 12.8 (Me3) 6.23 (s, 2H, H4,4%) 6.79 (m, 2H, CH2 of bpzm*+H4 of sal) 58.8 (CH2 of bpzm*) 109.3 (C4%) 7.02 (d, 1H, H6 of sal, JAB = 8.1) 7.35 (s, 1H, CH2 of bpzm*) 109.4 (C4) 7.61 (m, 1H, Hs of sal) 118.0 (C6 of sal) 7.76 (dd, 1H, H3 of sat J34 = 8.2 120.7 (C4 of sal) J35 =1.7) 122.5 (C2 of sal) 8.77 (s, 1H, CHO of sal) 137.5 (C3 of sal) 141.3 (C5 of sal) 145.1 (C5%) 145.2 (C5%) 154.1 (C3%) 154.5 (C3) 167.3 (Cl of sal) 190.8 (CO of sal)

6H, 6H, 6H, 1H, 2H, 1H, 1H,

139

Me of acac) Me3,3%) Me5,5%) CH of acac) H4,4%) CH2 of bpzm*) CH2 of bpzm*)

24 a 2.43 2.53 2.58 2.62 6.36 6.85 7.31 8.17

a b

(s, 3H, Me3%) (s, 3H, Me5%) (s, 3H, Me5) (s, 3H, Me3) (m, 2H, H4+H4 of 2-pcal) (d, 1H, CH2 of bpzm*, JAB =15,5) (m, 3H, CH2 of bpzm*+H3,5-2-pcal) (s, 1H, CHO of 2-pcal)

10.9 (Me5’) 11.2 (Me5) 12.6 (Me3%) 14.8 (Me3) 59.6 (CH2 of bpzm*) 108.8 (C4%) 109.8 (C4) 116.7 (C4 of 2-pcal) 126.8 (C3 of 2-pcal) 145.1 (C5%) 145.7 (C5%) 146.0 (C5 of 2-pcal) 146.2 (C2 of 2-pcal) 154.5 (C3%) 154.6 (C3) 183.8 (CO of 2-pcal)

In (CD3)2CO. In (CD3)2SO.

Complex 2: yield 80%. (Anal. Found: C, 30.7; H, 3.6; N, 14.0. Calc. for C15Cl2H22N6O8Pd: C, 30.4; H, 3.7; N, 14.2%). LM (S cm2 mol − 1) 257. IR (cm − 1) (Nujol): 2334, 2304 (CN str). [Pd(NN)(L)2][ClO4]2 (NN=bpzm: L=pyridine (3), triphenylphosphine (4), triethylphosphine (5) or L2 = 1,2-bis(diphenylphosphino)ethane (6), ethylenediamine (7), N,N,N%,N%-tetramethylethylenediamine (8), 2,2%-bipyridine (9), o-phenylendiamine (10); NN = bpzm*: L= pyridine (11), or L2 = 1,2-bis(diphenylphosphino)ethane (12), ethylenediamine (13), N,N,N%,N%-tetramethylethylenediamine (14), 2,2%-bipyridine (15), ophenylendiamine (16)). In separate experiments, the corresponding ligand (L or L2) was added in stoichiometric amount (1:1 for the bidentate ligands and 2:1 for the monodentate ligands) to 0.1 g of [Pd(NN)(CH3CN)2][ClO4]2 in acetone (20 cm3) and the solution was stirred for 1 h at room temperature. The solution was then concentrated under vacuum and the addition of diethyl ether determined the precipitation of the complexes as white or yellow solids, which were filtered off, washed repeatedly with diethyl ether and air-dried. The compounds were purified by recrystallization from (CH3)2COEt2O. Complex 3: yield 81%. (Anal. Found: C, 33.4; H, 2.1; N, 13.9. Calc. for C17Cl2H19N6O8Pd: C, 33.3; H, 2.9; N, 13.7%. LM (S cm2 mol − 1). IR (cm − 1) (Nujol): 1610 (py). Complex 4: yield 70%. (Anal. Found: C, 52.7; H, 3.1; N, 5.4. Calc. for C43Cl2H38N4O8P2Pd: C, 52.7; H, 3.8; N, 5.7%). LM (S cm2 mol − 1) 172. IR (cm − 1) (Nujol): 748, 540 (PPh3). 31P NMR in (CD3)2CO (300 MHz, H3PO4): d 30.8. Complex 5: yield 65%. (Anal. Found: C, 33.1; H, 5.5; N, 8.0. Calc. for C19Cl2H38N4O8P2Pd: C, 33.0; H, 5.6; N, 8.1%). LM (S cm2 mol − 1) 161. IR (cm − 1) (Nujol): 774, 608 (PEt3). 31P NMR in (CD3)2CO (300 MHz, H3PO4): d 34.7. Complex 6: yield 75%. (Anal. Found: C, 46.2; H, 3.2; N, 6.1. Calc. for C33Cl2H32N4O8P2Pd: C, 46.5; H, 3.7; N, 6.5%). LM (S cm2

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mol − 1) IR (cm − 1) (Nujol): 510 (dppe). Complex 7: yield 69%. (Anal. Found: C, 21.3; H, 3.2; N, 16.5. Calc. for C9Cl2H16N6O8Pd: C, 21.0; H, 3.1; N, 16.3%). LM (S cm2 mol − 1) 163. IR (cm − 1) (Nujol): 3516, 3500 (NH str). Complex 8: yield 80%. (Anal. Found: C, 27.5; H, 4.0; N, 14.5. Calc. for C13Cl2H24N6O8Pd: C, 27.3; H, 4.2; N, 14.7%). LM (S cm2 mol − 1) 159. Complex 9: yield 75%. (Anal. Found: C, 33.1; H, 2.3; N, 13.4. Calc. for C17Cl2H16N6O8Pd: C, 33.4; H, 2.6; N, 13.7%). LM (S cm2 mol − 1) 159. Complex 10: yield 72%. (Anal. Found: C, 27.9; H, 2.8; N, 14.7. Calc. for C13Cl2H16N6O8Pd: C, 27.8; H, 2.8; N, 14.4%). LM (S cm2 mol − 1) 131. IR (cm − 1) (Nujol): 3234, 3204 (C6H4(NH2)2). Complex 11: yield 86%. (Anal. Found: C, 37.4; H, 3.5; N, 12.3. Calc. for C21Cl2H26N6O8Pd: C, 37.7; H, 3.8; N, 12.5%). LM (S cm2 mol − 1) 196. IR (cm − 1) (Nujol): 1608, 3204 (py). Complex 12: yield 80%. (Anal. Found: C, 48.7; H, 4.4; N, 8.6. Calc. for C37Cl2H40N4O8P2Pd: C, 48.9; H, 4.4; N, 8.4%). LM (S cm2 mol − 1) 143. IR (cm − 1) (Nujol): 532, 510 (dppe). 31P NMR in (CD3)2SO (300 MHz, H3PO4): d 57.6. Complex 13: yield 68%. (Anal. Found: C, 27.6; H, 4.0; N, 14.4. Calc. for C13Cl2H24N6O8Pd: C, 27.4; H, 4.2; N, 14.4%). LM (S cm2 mol − 1) 171. IR (cm − 1) (Nujol): 3510, 3500 (NH str). Complex 14: yield 76%. (Anal. Found: C, 32.5; H, 5.2; N, 13.4. Calc. for C17Cl2H32N6O8Pd: C, 32.6; H, 5.1; N, 13.4%). LM (S cm2 mol − 1) 172. IR (cm − 1) (Nujol): 804, 774 (tmeda). Complex 15: yield 80%. (Anal. Found: C, 38.0; H, 3.6; N, 12.4. Calc. for C21Cl2H24N6O8Pd: C, 37.8; H, 3.6; N, 12.6%). LM (S cm2 mol − 1) 162. IR (cm − 1) (Nujol): 1612 (CN str). Complex 16: yield 70%. (Anal. Found: C, 33.3; H, 3.7; N, 13.9. Calc. for C17Cl2H24N6O8Pd: C, 33.0; H, 3.9; N, 13.6%). LM (S cm2 mol − 1) 178. IR (cm − 1) (Nujol): 3238, 3208 (C6H4(NH2)2).

2.2.3. [Pd(NN)(LL)][ClO4] (NN= bpzm: LL= acetylacetonate (19), salicylaldehydate (20), 2 -pyrrolcarbaldehyde (21); NN = bpzm*: LL= acetylacetonate (22), salicylaldehydate (23), 2 -pyrrolcarbaldehyde (24) The corresponding protic electrophile (Hacac, Hsal, H2-pcal) was added in a molar ratio of 2:1 to a suspension of [Pd2(NN)2(m-OH)2][ClO4]2 (0.1 g, NN = bpzm or bpzm*) in acetone (10 cm3). After stirring at room temperature for 1 h, the resulting solution was concentrated under reduced pressure. Addition of Et2O caused the precipitation of the complexes 19–24 as yellow solids which were filtered off, air-dried and recrystallized from (CH3)2CO/Et2O. Complex 19: yield 78%. (Anal. Found: C, 31.4; H, 3.7; N, 12.3. Calc. for C14ClH13N4O6Pd: C, 34.7; H, 2.7; N, 11.6%). LM (S cm2 mol − 1) 132. IR (cm − 1) (Nujol): 1562, 1525 (acac). Complex 20: yield 81%. (Anal. Found: C, 34.3; H, 2.4; N, 11.3. Calc. for C12ClH8N4O6Pd: C, 31.2; H, 3.2; N, 12.1%). LM (S cm2 mol − 1) 117. IR (cm − 1) (Nujol): 1612, 1586, 1570 (sal). Complex 21: yield 74%. (Anal. Found: C, 32.5; H, 2.8; N, 15.4. Calc. for C12ClH12N5O5Pd: C, 32.2; H, 2.7; N, 15.6%). LM (S cm2 mol − 1) 112. IR (cm − 1) (Nujol): 1566 (2-pcal). Complex 22: yield 75%. (Anal. Found: C, 37.4; H, 4.1; N, 11.1. Calc. for C16ClH23N4O6Pd: C, 37.0; H, 4.4; N, 10.8%). LM (S cm2 mol − 1) 128. IR (cm − 1) (Nujol): 1562, 1525 (acac). Complex 23: yield 70%. (Anal. Found: C, 39.8; H, 4.0; N, 10.4. Calc. for C18ClH21N4O6Pd: C, 40.0; H, 3.9; N, 10.4%). LM (S cm2 mol − 1) 115. IR (cm − 1) (Nujol): 1614, 1590, 1574

2.2.2. [(NN)Pd(m-OH)2Pd(NN)][ClO4]2 (NN = bpzm (17), bpzm* (18)) To an acetone (20 cm3) suspension of [Pd(NN)Cl2] (0.2 g) was added a stoichiometric amount of AgClO4 (molar ratio 1:2). The mixture was then boiled under reflux for 1/2 h. After removal of the precipitated AgCl and slow addition of water (approximately 100 ml), the solution was stirred at room temperature for 5 h. The yellow compounds obtained in this way were filtered off, washed with diethyl ether and air-dried. Complex 17: Yield 60%. (Anal. Found: C, 22.7; H, 2.1; N, 15.1. Calc. for C14Cl2H18N8O10Pd2: C, 22.6; H, 2.4; N, 15.1%). LM (S cm2 mol − 1) 143. IR (cm − 1) (Nujol): 3380 (OH str). FAB-MS (positive mode) in NBA. Ions (m/z): [{Pd(bpzm)(OH)}2]+ – 1 (543), [Pd(bpzm)2(OH)]+ (419), [Pd(bpzm)(OH)]+ (271). Complex 18: yield 81%. (Anal. Found: C, 22.7; H, 2.1; N, 15.1. Calc. for C22Cl2H34N8O10Pd2: C, 22.6; H, 2.4; N, 15.1%). LM (S cm2 mol − 1) 157. IR (cm − 1) (Nujol): 3424 (OH str). FAB-MS (positive mode) in NBA. Ions (m/z): [{Pd-

Scheme 2. Labeling scheme for the bis(pyrazoyl)-methane ligand and the boat-to-boat inversion.

(bpzm*)}2-(OH)(NBA)]+ (790), [{Pd(bpzm*)(OH)}2(ClO4)]+ (754), [Pd(bpzm*)(OH)}2]+ (654), [{Pd(bpzm*)}2(OH)]+ (638).

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(sal). Complex 24: yield 81%. (Anal. Found: C, 38.5; H, 2.5; N, 14.5. Calc. for C16ClH20N5O5Pd: C, 38.6; H, 2.8; N, 14.7%). LM (S cm2 mol − 1) 121. IR (cm − 1) (Nujol): 1574 (pcal).

2.3. X-ray data and crystal structure determination Suitable crystals of the complexes 8·H2O and 23 were obtained from acetone – hexane. Crystallographic data for both complexes are collected in Table 1. A crystal of 8·H2O was mounted on a glass fiber and transferred to the diffractometer (Siemens P4 with LT2 low-temperature attachment). The scan method was v with the range of hkl (−135h 513, − 16 5k 5 16, 05 l5 17) corresponding to 2umax =50.02°. Empirical C-scan mode absorption was made. 7737 reflections were collected, 3728 were unique (Rint =0.050). In 23 data were collected on an Enraf – Nonius CAD 4 diffractometer with a graphite monochromator for Mo Ka radiation. The scan method was v – 2u with the range of hkl (− 115h5 11, −15 5k 5 14, −19 5l5 0) corresponding to 2umax =60.88°. Empirical C-scan mode absorption was made. The structures were solved by the heavy atom method and refined by full-matrix least-squares techniques SHELXL-93 [27] using anisotropic thermal parameters for non-hydrogen atoms. In 8·H2O solvent hydrogen atoms were located in a difference Fourier synthesis and refined with a restrained OH bond length. Other hydrogen atoms were included using a riding model or as rigid methyl groups. In 23 all the hydrogen atoms were introduced in calculated positions. In 8·H2O the absolute structure was determined (Flack parameter x =0.04(3)) [28]. A large peak at 0.925 A, from the palladium center is probably due to a poor absorption correction. Maximum D/s =0.001, maximum Dr =1.57 e A, − 3. The final R factors were 0.0287 and 0.0519 in 8·H2O and 23, respectively (Rw = 0.0648 and 0.1396, w =1/[s 2(F 2) + (aP)2 +bP] where P= (F o2 + 2F c2)/3 and a and b are constants set by the program) over the observed reflections [I \2s(I)].

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The IR spectra of compounds 1 and 2 exhibit two sharp absorptions in the CN stretching frequency region, commonly interpreted [29,30] as the CN stretching vibration (at approximately 2300 cm − 1) and a combination band of CC stretching and CH3 deformation (at approximately 2330 cm − 1). In free acetonitrile these bands are found at 2254 and 2290 cm − 1, respectively. Other relevant absorptions observed in these and the remaining compounds are those corresponding to the perchlorate anion [31] (n3 ClO4) at approximately 1080 cm − 1 and those attributed to bis(pyrazol-1-yl)methane ligands. The high lability of the acetonitrile ligand in the new compounds hampered their study in solution. The 1 H NMR spectra suggested the existence of the equilibrium [Pd(NN)(CH3CN)2]2++xsolv ? [Pd(NN)(CH3CN)2−x (solv)x ]2 + + xCH3CN, in which acetonitrile is replaced by molecules of the deuterated solvent (solv). Even when the spectra were recorded in deuterated acetonitrile, a complex set of time-dependent signals was observed in the aromatic region corresponding to the NN ligands, and various signals appeared in the high-field methyl region.

3. Results and discussion

3.1. Synthesis and characterization of complexes [Pd(NN)L2] 2 + The solvento complexes [Pd(NN)(CH3CN)2]2 + (NN = bpzm (1) or bpzm* (2)) were made by treating [Pd(NN)Cl2] with 2 equiv. of AgClO4 in acetonitrile. After elimination of the precipitated AgCl, 1 and 2 were isolated as the perchlorate salts (Scheme 1). On standing in air, both complexes gradually become pale brown solids, but they do not readily decompose extensively.

Scheme 3.

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Fig. 1. Structure of the [Pd(bpzm)(tmeda)]2 + cation. Selected bond lengths (A, ) and angles (°): PdN(4) 2.040(3), PdN(1) 2.061(3), PdN(5) 2.063(3), PdN(6) 2.072(3), N(4)PdN(1) 85.57(11), N(4)PdN(5) 93.86(12), N(1)PdN(6) 95.48(12), N(5)PdN(6) 85.16(12), N(3)C(4)N(2) 109.2(3).

Scheme 4.

The addition of the corresponding ligands to the precursors Pd(NN)(CH3CN)2][ClO4]2 in acetone leads to the formation of complexes 3 – 16 shown in Scheme 1. Although similar reactivity was expected for both acetonitrile complexes, their behavior against the tested ligands was not the same. Thus, the bis(3,5-dimethylpyrazolyl)methane precursor does not react with the monodentate phosphines PPh3 and PEt3, probably due to the additional hindering produced by the 3- and 5-methyl groups on each pyrazolyl ring. Only the bidentate phosphine dppe coordinates to palladium in the presence of the bpzm* ligand. The isolated compounds are white or pale yellow air-stable solids, soluble in common organic solvents but insoluble in diethyl ether and hexane. Their acetone solutions exhibit conductance values corresponding to 2:1 electrolytes [32]. The dppe derivatives are only slightly soluble in acetone or dichloromethane and their solution-study was carried out in dimethylsulphoxide. Infrared spectra of all compounds showed the characteristic absorptions of the ClO4 − anion at approximately 1100 cm − 1 and the NN ligands (bpzm: 1520 cm − 1, bpzm*: 1555 cm − 1). In Section 2 are also collected the most relevant bands assigned to the neutral N- and P-donor ligands. The NMR data of complexes 3 – 16 are collected in Table 2. In accordance with the presence of the symmetrical bpzm or bpzm* ligands containing two equivalent pyrazolyl rings, only one set of 1H resonance signals is observed in the spectra, together with resonances assigned to N- and P-donor ligands. In complexes 3–10, when no overlapping of signals is

operating, the experimental NMR pattern observed is one doublet at d 8.5–7.4 for H3,3%, one doublet at d 8.5–7.9 for H5,5% and a pseudo triplet (doublet of doublets) at d 7.0–6.0 for H4,4% (see Scheme 2 for the proton labeling). The assignment of the H3,3% and H5,5% resonances was made by NOE experiments, which pointed out a clear NOE effect between the CH2 resonance and the signal consequently assigned to H5,5%. The general rule J45 \ J34, usually observed in non-coordinated pyrazols [33] and in previous studies with ruthenium [4c] and palladium [11] complexes, is also followed in our compounds. Compounds 11–16 show two singlet resonances in the aliphatic region attributed to the Me3,3% (d 2) and Me5,5% (d 2.5) groups, respec-

Fig. 2. Structure of the cation of complex 23. Hydrogen atoms have been omitted for clarity. Selected bond lengths (A, ) and angles (°): PdN(1) 2.009(4), PdN(2) 2.025(4), PdO(1) 1.952(3), PdO(2) 1.987(4), N(2)PdN(1) 88.6(2), N(2)PdO(1) 89.53(14), N(1)PdO(2) 87.8(2), O(1)PdO(2) 94.1(2), N(3)C(13)N(4) 109.4(4).

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signed using 1H– 13C HETCOR experiments and comparison with previously reported data.

3.2. Synthesis of [Pd2(NN)2(m-OH)] 2 + and their reacti6ity towards acidic reactants H(LL)

Fig. 3. Packing diagram showing the hydrogen bonding in compound 8·H2O. Selected H-bond lengths (A, ) and angles (°): H(02)O(1) 2.112(35), O(9)O(1) 2.921(4), O(9)H(02)O(1) 167.95(4.69); H(01)O(4A) 2.506(47), O(9)O(4A) 3.140(5), O(9)H(01)O(4A), symmetry transformation to generate the atoms denoted A is −x + 3/2, −y − 1, z−1/2.

tively, and one singlet for H4,4% (d 6.3). In complexes with the bpzm* ligand, the diastereotopic protons of the bridging CH2 group give two signals corresponding to an AB spin system; this is also the case for complexes 8 and 9 with the bpzm ligand, indicating that the boat-to-boat inversion process [8] represented in Scheme 2 is frozen at room temperature. The observation of a single methylene signal in the 13C{1H} NMR spectra (Table 2) dismisses the possibility of a mixture of isomers or dissociation in solution. However, the single resonance observed for the two methylene protons in the spectra of the bpzm compounds 3 – 7 and 10 indicates that fast inversion occurs at room temperature. The 13C and 31P NMR data (see Table 2 and Section 2) are all consistent with the structures of the new compounds. The 13C resonances have been as-

Fig. 4. Relevant dihedral angles in the boat conformation of the cations in complexes 8 and 23.

When the reaction was carried out in acetone (Scheme 3), stronger conditions were needed to achieve complete precipitation of silver chloride. Addition of water to the filtered solution and further stirring produced the precipitation of the new hydroxo-bridged dimers [Pd(m-OH)(NN)]2[ClO4]2. The attainment of such a bridged dimer was not unexpected, since similar reactions have been previously reported for complexes with neutral P-donor ligands [34] or NN chelate ligands [35–37]. The IR spectra of compounds 17 and 18 show the bands mentioned above, assigned to the perchlorate anion and the neutral NN chelate ligands, together with absorptions of the hydroxo groups at 3380 and 3424 cm − 1 (OH str) [36,37], and 466 and 450 cm − 1 (PdOH str) [38,39], respectively. The OH bending mode, usually observed in the region 1100–900 cm − 1, should be obscured by the broad, intense absorption of the ClO4 − anion. Poor solubility in most of the usual solvents hampered full characterization of the new hydroxo complexes. Their NMR study was carried out in DMSO-d6, in which the complexes were slightly soluble. Although the overall pattern of the spectra is similar to that for the free ligands and dichloride precursors [8], a loss of multiplicity in signals is observed due to solvent effects, resulting in broad singlet resonances. As regard to the methylene NMR signals shown by the compounds, depending on the different bpzm or bpzm* ligand, we found the same behavior previously reported [4,8,11] for bis(pyrazol-1yl)methane ligands. Thus, in the spectrum of 17 at room temperature, the CH2 protons appear as a singlet, indicating that inversion of the metallocycles Pd(NN)2C is fast on the NMR time scale. In complex 18, where CH3 substituents are present, the molecules become less flexible and the CH2 protons display a wellresolved AB system at room temperature. No proton resonance attributable to the bridging OH protons was observed in the high field region of the 1H NMR spectra of complexes 17 and 18 [40]1, which may be a consequence of proton exchange with solvent and/or the existence of hydrogen bonding. The IR spectra also suggest the presence of hydrogen bonding in the solid state because the OH stretching bands reported above

1 In [Pd2(C6F5)4(m-OH)2]2 – and [Pd2(C6F5)4(m-OH)(m-pyrazolate)]2 – the m-OH proton resonance is found at d − 2.84 and d − 1.53, respectively.

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are usually found at higher wavenumbers in hydroxobridged dimeric compounds; for instance, at 3610 cm − 1 in [M2(C6F5)4(m-OH)2]2 − (M =Pd [36] or Pt [41]). Direct evidence for the dinuclearity of complexes 17 and 18 comes from FAB-mass spectrometry. The positive FAB-MS data of the complexes, with m/z values for the expected fragments are collected in Section 2. Spectra of both compounds show as most outstanding feature the peaks corresponding to [Pd2(NN)2(OH)2]+ at m/z 543 (complex 17) and 654 (complex 18). The abundances of the signals around the parent ion are consistent with the natural isotopic abundances. The additional peaks observed indicate further fragmentation and formation of some adducts with the matrix [42]. The basic character of complexes 17 and 18 is consistent with the chemical reactivity exhibited toward protic electrophiles, H(LL), to give the mononuclear complexes 19–24 shown in Scheme 3. The acidic proton of the corresponding acids (acetylacetone, salicylaldehyde or 2-pyrrolcarbaldehyde) is abstracted by the {Pd(m-OH)2Pd} fragment giving the new complexes, with the concomitant release of water. These acid –base reactions take place at room temperature and complexes 19–24 are recovered by precipitation with diethyl ether. The new complexes are air-stable solids and their analytical data, molar conductivities (in the range 112–132 corresponding to 1:1 electrolytes [32]) and relevant IR absorptions are collected in Section 2. 1H and 13C NMR spectra of complexes 19–24 (Table 2) show the respective signals of the acetylacetonate (acac), salicylaldehydate (sal) and 2-pyrrolcarbaldehydate (2-pcal) ligands, together with the corresponding resonances of the pyrazolyl groups. Depending on the growing asymmetry of the complexes (acac B salB2-pcal), the two pyrazolyl groups were identical or spectroscopically different. Thus, the pyrazolyl NMR signals for the 2-pcal complexes, both in 1 H and 13C spectra, were clearly classified into two sets; an intermediate situation appeared in the sal complexes, while a single set characterized the acac complexes as expected in a situation of high symmetry. When a split of signals is observed, it is more pronounced for protons or methyl groups in position 3 (bpzm or bpzm* complexes), where the effect of different trans surrounding is higher than in positions 4 or 5, in this order. In compounds 20 and 21 the two sets of protons H3,4,5 and H3%,4%,5% were clearly assigned by means of homonuclear double resonance experiments. Selective irradiation of the pseudo triplets (labeled 4 and 4%) caused a loss of multiplicity and enhancement of signals of the corresponding coupled protons, H3,5 or H3%,5%, respectively. In these compounds it was also possible to identify the relative position of every pyrazolyl ring trans to N or O on the basis .

of NOE experiments, which showed the dipolar coupling between H3 of bpzm and H5 of 2-pcal (Scheme 4). From all experiments performed, it can be assumed that the set of pyrazol signals which appear at a higher field [H3 (or Me3), H4 and H5 (or Me5)] corresponds to the ring trans to the deprotonated atom: nitrogen in 21 and 24 or alcoholic oxygen in 20 and 23 (Scheme 4). The assignment of 13C resonances has been made by 1H– 13C heteronuclear correlations (HETCOR).

3.3. Crystal structures of [Pd(bpzm)(tmeda)][ClO4]2 (8) and [Pd(bpzm*)(sal)][ClO4] (23) The molecular structures of [Pd(bpzm)(tmeda)][ClO4]2 (8) and [Pd(bpzm*)(sal)][ClO4] (23) have been determined by X-ray diffraction studies and are presented in Figs. 1 and 2, respectively, together with some selected bond distances and bond angles. The structure of 8 contains [Pd(bpzm)(tmeda)]2 + cations held together with ClO4 − anions by electrostatic interactions. A water molecule is trapped in the structure, connected by intermolecular hydrogen bond with two perchlorates (distance ClO···H, 2.039 A, ; Fig. 3). The coordination around the Pd(II) atom is slightly distorted from the ideal square-planar geometry; the distortion is indicated, for instance, by the dihedral angle between the N(1)PdN(4) and N(5)PdN(6) planes and by the N(1)PdN(5) and N(4)PdN(6) angles which depart significantly from 180°. The molecule has optical isomerism and the absolute configuration for the crystal was determined (Flack parameter= −0.04) [28]. In the structure of the [Pd(bpzm*)(sal)]+ cation of 23, the Pd atom and the four atoms coordinated to it deviate slightly from the mean plane defined by them. As expected, the two PdN distances (2.005 and 2.026 A, ) are quite close to the PdO distances (1.955 and 1.986 A, ), the distance between the Pd and the deprotonated oxygen being the shortest. The angles around Pd deviate from the square-planar coordination as the effect of different bidentate ligands produces an increase of the O(1)PdO(2) angle (94.13°) and a similar shortening of N(1)PdN(2) (88.58°). The PdN(pyrazolyl) distances in 8 are longer than the corresponding distances in 23 but they are similar to those found in the binuclear [Pt2(C6F5)4(m-OH)(m-3,5-dimethylpyrazolate)]2 − anion (Pt1N1 = 2.04(1), Pt2N2 =2.075(9) A, ) [43]. However, longer MN distances (PdN = 2.103(5), PtN =2.091(5) A, ) are found in the [M(C6F5)2(pz)(Hpz)]− anions (M= Pd, Pt) containing two pyrazolate (pz) rings bridged by an intramolecular hydrogen bond (pz···H···pz) [44]. The boat conformation adopted by the central CNNPdNN ring of the cations in 8 and 23 is explicitly shown in Fig. 4.

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4. Supplementary material Tables giving atomic coordinates and equivalent isotropic displacement parameters, extended lists of bond distances and bond angles, anisotropic displacement parameters for non-hydrogen atoms, final observed and calculated structure factors and isotropic displacement parameters for hydrogen atoms may be obtained directly from the authors on request.

Acknowledgements Financial support from the Direccio´n General de Investigacio´n Cientı´fica y Te´cnica (project PB97-1036), Spain, is gratefully acknowledged. J.L. Serrano and J. Pe´re´z thank CajaMurcia and Ministerio de Educacio´n y Ciencia, respectively, for research grants.

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