Reactions of metallabromoalkanes [M{(CH2)nBr}(CO)3(η-C5H5)](M = Mo or W, n= 3 or 4) with transition metal anions. Dimetalla-alkane and cyclic carbene complex formation. Crystal and molecular structures of [(η-C5H5)(OC)3Mo{(CH2)4}Mo(CO)3(η-C5H5)] and [(η-C5H5)(OC)3MoW(CO)2{C–O–(CH2)2CH2}(η-C5H5)]

Abstract

Reaction of Br[CH₂]₃Br with excess [Mo(CO)₃(η-C₅H₅)]^– leads to the spectroscopically characterised [(η-C₅H₅)(OC)₃MoMo(CO)₂{[graphic omitted]H₂}(η-C₅H₅)] containing a cyclic carbene ligand. This species is formed via the intermediate [Mo{(CH₂)₃Br}(CO)₃(η-C₅H₅)]. The related complex [(η-C₅H₅)(OC)₃MoW(CO)₂{[graphic omitted]H₂}(η-C₅H₅)] is formed during reaction of [Mo{(CH₂)₃Br}(CO)₃(η-C₅H₅)] with [W(CO)₃(η-C₅H₅)]^– and has been characterised by X-ray crystallography. This molecule crystallises as maroon needles, monoclinic, a= 8.017(6), b= 15.026(16), c= 7.981 (3)Å, β= 92.88(5)°; R converged to 0.0645 for 1 256 independent reflections for which I/σ(I) > 3.0. The molecule contains a Mo–W single bond of 3.239(4)Å, the cyclic carbene ligand is bonded to tungsten rather than molybdenum and is situated trans to the Mo–W bond regarding the co-ordination polyhedra of both metals as square-based pyramidal. Reaction of [M(CO)₃(η-C₅H₅)]^– with I[CH₂]_nI leads to [(η-C₅H₅)(OC)₃M{(CH₂)_n}M(CO)₃(η-C₅H₅)](M = Mo, n= 4; M = W, n= 3 or 4). The structure of one member of this class [(η-C₅H₅)(OC)₃Mo{(CH₂)₄}Mo(CO)₃(η-C₅H₅)] has been determined by X-ray crystallography. The molecule crystallises as yellow elongated plates, triclinic, a= 6.978 2(16), b= 7.005 1(10), c= 11.315 0(25)Å, α= 102.378(15), β= 95.806(18), γ= 105.909(15)°; R converged to 0.0263 for 1 646 independent reflections. The molecule contains a crystallographically imposed centre of symmetry at the centre of the tetramethylene chain and the molecular structure may be compared to that of the known [(η-C₅H₅)(OC)₂Fe{(CH₂)₄}Fe(CO)₂-(ηC₅H₅)].