Linear Metal-Metal-Bonded Tetranuclear M-Mo-Mo-M Complexes (M = Ir and Rh):Oxidative Metal-Metal Bond Formation in a Tetrametallic System and 1,4-Addition Reaction of Alkyl Halides

摘要

Reaction of Mo2(pyphos)4 (1) with [MCI(CO)2]2 (M = Ir and Rh) afforded linear tetranuclear complexes of a formula Mo2M2(CO)2(CI)2(pyphos)4 (2,M = Ir;3,M = Rh).X-ray diffraction studies confirmed that two "MCI(CO)" fragments are introduced into both axial sites of the Mo2 core in 1 and coordinated by two PPh2 groups in a trans fashion,thereby forming a square-planar geometry around each M(l) metal.Treatment of 2 and 3 with an excess amount of tBuNC and XylNC induced dissociation of the carbonyl and chloride ligands to yield the corresponding dicationic complexes [Mo2M2(pyphos)4(tBuNC)4](CI)2 (5a,M = Ir;6a,M = Rh) and [Mo2M2(pyphos)4(XylNC)4](Cl)2 (7,M = Ir;8,M = Rh).Their molecular structures were characterized by spectroscopic data as well as X-ray diffraction studies of BPh4 derivatives [Mo2M2(pyphos)4(tBuNC)4](BPh4)2 (5b,M = Ir;6c,M = Rh),which confirmed that there is no direct sigma-bonding interaction between the M(l) atom and the Mo2 core.The M(l) atom in 5 and 6 can be oxidized by either 2 equiv of [Cp2Fe][PF6] or an equimolar amount of l2 to afford Mo(ll)2M(ll)2 complexes,[Mo2M2-(X)2(tBuNC)4(pyphos)4]~(2+) in which two Mo-M(ll) single bonds are formed and the bond order of the Mo-Mo moiety has been decreased to three.The lr(l) complex 5a reacted not only with methyl iodide but also with dichloromethane to afford the 1,4-oxidative addition products [Mo2lr2(CH3)(l)(tBuNC)4(pyphos)4](CI)2 (13) and [Mo2lr2(CH2CI)(CI)(t-BuNC)4(pyphos)4](CI)2 (15),respectively,although the corresponding reactions using the Rh(l) analogue 6 did not proceed.Kinetic analysis of the reaction with CH3I suggested that the 1,4-oxidative addition to the lr(l) complex occurs in an SN2 reaction mechanism.