Molybdenum-hydrazido(2−) complexes with tridentate thiolate ligands

Abstract

Recent EXAFS [1] studies of nitrogenase and other molybdo-proteins have stimulated interest in molybdenum complexes with sulfur ligands. However, none of the complexes so far reported bind or activate dinitrogen. In fact, there are very few examples of molybdenumsulfur complexes which interact with small molecules that can function as inhibitors or alternative substrates for nitrogenase or indeed with any ligands relevant to nitrogen fixation. Hydrazido(2−) complexes are proven intermediates in both protonation [2] and the alkylation ▪ [3] or coordinated dinitrogen. This paper reports their use to probe the properties of a molybdenum site ligated to thiolate-containing ligands of the type L = HSCH 2CH 2XCH 2CH 2SH 2, where X = NR, PR, O, and S. t001 Comparison of MoNN Geometries in Molybdenum-hydrazido and Molybdenum-diazenido Complexes, Complex MoN NN MoNN Ref. a. Six coordinate Mo [MoO(N 2R 2)(dtc) 2] a 1.799 1.29 168.0 7 [Mo(N 2Ph 2)(dtc) 2] 1.790 1.31 169.9 8 [Mo(N 2PhMe) 2(dtc) 2] 1.790 1.30 172.6 9 [MoO(N 2Ph 2)(S 2N 2)] b 1.778 1.309 172.9 10 [Mo(N 2Ph)(S 2N 2)] 1.82 1.28 170.4 10 [MoO(N 2Me 2)(C 9H 6NO) 2] 1.800 1.28 155.5 11 [S 2MoS 2Mo(N 2Me 2) 2S 2MoS 2] 2− 2.15 1.19 167.0 12 b. Seven coordinate Mo [Mo(N 2Ph)(dtc) 3] 1.781 1.233 171.5 13 [Mo(N 2PhEt)(dtc) 3] + 1.715 1.37 170.0 14 [Mo(N 2MePh)(NHHMePh)(dtc) + 2 1.75 1.29 169.6 15 [Mo(N 2CO 2Me)(NHNHCO 2Me)(dtc) 2] 1.74 1.30 177.1 16 [Mo(NNMe 2)(SPS)] e 1.775 1.265 178.3 c. Five coordinate Mo [MoO(N 2Me 2)(SPh) 3] + 1.806 1.30 176.7 17 [MoO(N 2Me 2)(SSS)] c 1.78 1.29 176.2 18 [MoO(N 2Me 2)(SOS)] 1.79 1.29 174.3 This work [MoCl(N 2Me 2) 2(PPh 3) 2] + 1.761 1.25 173.9 19 [S 2MoS 2Mo(N 2Me 2) 2(PPh 3) 2] 1.78 1.30 165.0 20 1.80 1.27 178.2 a dtc = dithiocarbamate, (S 2CNR 2) −. b S 2N 2 = (SCH 2CH 2NRCH 2CH 2NRCH 2CH 2S) −. c SSS = (SCH 2CH 2SCH 2CH 2S) 2−. e SPS = (SCH 2CH 2PPLCH 2CH 2S) 2−. ▪ ▪ The synthesis and structural characterization of the precursor species Mo 2O 3L 2, where X = NR, O and S have been described elsewhere [4, 5]. Reactions of these complexes with phenylhydrazine result in the isolation of yellow, diamagnetic monomers MoO(NNHC 6H 5)L, I, whose structure is illustrated in Fig. 1. Reaction of I with Me 3SiCl in dry methanol results in protonation of the hydrazido-ligand to give the hydrazido(1−) species, [MoO(N 2H 2Ph)L] +, III, isolated as the BPh − 4 salt. Protonation appears to occur at the metal-bound nitrogen to give the dihapto-coordination type previously described for [Mo(dtc) 3(NNMePh)] BPh 4 [6], shown schematically in Fig. 2. Reactions of the precursor materials with disubstituted hydrazines, such as H 2NNMe 2, yield exclusively bis-hydrazido(2−) complexes, of the type Mo(NNMe 2) 2L, deep purple, diamagnetic monomeric materials, whose structural identification is in progress. When L is −SCH 2CH 2PPhCH 2CH 2S −, the major product isolated upon reaction of the molybdenum precursor with disubstituted hydrazine is [Mo(NNMe 2)L 2], II, a seven coordinate diamagnetic monomer, whose coordination geometry is illustrated in Fig. 3. The geometry of the molybdenum-hydrazido(2−) grouping is similar both I and II. Linear MoNN moieties, with considerable double bond character in both the MoN and NN bonds, are common to the structural chemistry of molybdenum-hydrazido(2−) species, as illustrated in Table I. The exceptions to the common geometric type [Mo 3S 8(NNMe 2) 2] 2− [7] and [MoO(NNPh 2)(oxime) 2] [8] show unusual protonation chemistry and suggest that the course of protic degradation reactions of metal-bound hydrazides are sensitive to the MNN geometry. Crystal Data. Complex I, MoC 10H 14O 2N 2S 2, crystallizes in the triclinic space group P1 with a = 9.307(2) Å, b = 11.108(3) Å, c = 14.139(3) Å, α = 89.7(1)°, β = 91.88(1), γ = 107.91(2)°, V = 1390.0(9) Å 3 and Z = 4 to give D calc = 1.69 g cm −3 and μ = 12.15 cm −1 (MoKα, λ = 0.71069 Å. A total of 1956 reflections with I ⩾ 3.0σ( I) formed the basis for a full-matrix least squares refinement. Analysis converged at R = 0.045 and R w = 0.042, with a ‘goodness of fit’ of 1.21.