Reactions of co-ordinated ligands. Part 48. Reactivity studies of the octatrienediylidenedimolybdenum complexes [Mo2(µ-C8Me8)(η-C5H5)2] and [Mo2(µ-C8H4But4)(η-C5H5)2]. Crystal structures of [Mo2(µ-C8Me7CH2)(η-C5H5)2][CF3SO3], [Mo2(µ-C8Me8)(µ-Cl)(η-C5H5)2][SbCl4]·CH2Cl2, and [Mo2(µ-C8H4But4)(µMo,C-H)(η-C5H5)2][BPh4]·CH2Cl2

Abstract

Double protonation of [Mo₂(µ-C₈Me₈)(η-C₅H₅)₂], (1), with excess CF₃SO₃H or hydride abstraction with [CPh₃][BF₄] affords the cationic complex [MO₂(µ-C₈Me₇CH₂)(η-C₅H₅)₂]⁺, (4), which has been characterised as the triflate (CF₃SO₃) salt by X-ray crystallography. The structure of (4) is similar to that of (1) in having a C₈ chain bridging a Mo–Mo bond, the chain beginning and ending with σ bonds to Mo(2). Carbons C(1)–C(3) and C(6)–C(8) each form an η³-allylic interaction with Mo(1) and C(4), C(5), and C(9) bond in a similar manner to Mo(2)[in contrast to an η²-alkene-type interaction involving C(4) and C(5) found in (1)]. Mechanistic and electrochemical studies pertinent to the formation of (4) are discussed. Compound (4) reacts with the nucleophiles K[BHBu³₃], K[BDBu³₃], Li[CuMe₂], Li[CuPh₂] and Na[SMe] affording the neutral complexes [Mo₂(µ-C₈Me₇CH₂R)(η-C₅H₅)₂][R = H, (1); D, (1d); Me, (5); Ph, (6); or SMe, (7)] thereby enabling a modification of the δ-ring substituent in the original complex (1). Subsequent hydride abstraction from (5) results in the cation [Mo₂(µ-C₈Me₆EtCH₂)(η-C₅H₅)₂]⁺, (8), analogous to (4), which on treatment with Li[CuMe₂] affords the diethyl derivative [Mo₂(µ-C₈Me₆Et₂)(η-C₅H₅)₂], (9). The reaction of (1) with [NPrⁿ₄][SbCl₆] affords the chloro cationic species [MO₂(µ-C₈Me₈)(µ-Cl)(η-C₅H₅)₂]⁺, (11), which was characterised by X-ray crystallography. Its structure is very similar to that of (1) except in containing a chlorine bridging the Mo–Mo vector. Protonation of the unsymmetrically substituted complex [MO₂(µ-C₈H₄Bu^t₄)(η-C₅H₅)₂], (3), has also been studied and shown to afford a cationic complex containing an agostic CH interaction [Mo₂(µ-C₈H₄Bu^t₄)(µ_Mo,c-H)(η-C₅H₅)₂]⁺, (12). Compound (12) was characterised by X-ray crystallography which reveals the site of protonation on a δ-ring carbon in contrast to the α-protonation observed in [Mo₂(µ-C₈Me₈)(µ_Mo,c-H)(η-C₅H₅)₂]⁺, (2). Proton and ¹³C n.m.r. studies indicate, however, that the proton in (12) is fluxional between the α and δ sites analogous to that seen in (2). Details of the spectroscopic studies are presented and discussed.