Synthesis, Structure, and Reactivity of Polymetallic C₃OMe Complexes of the Formula (η⁵-C₅Me₅)Re(NO)(PPh₃)(C⋮CC(OMe))M<i>_m</i>(CO)<i>_n</i> (M/<i>m</i>/<i>n</i> = Re/2/9, Os/3/11): A New Form of Coordinated Carbon in Which a C₃ Chain Links Two Metals and Spans a Third

Abstract

Reaction of (η5-C5Me5)Re(NO)(PPh3)(C⋮CLi) with Re2(CO)10 and then Me3O+BF4- gives the trirhenium C3OMe complex cis-(η5-C5Me5)Re(NO)(PPh3)(C⋮CC(OMe))Re(CO)4Re(CO)5 (3, 92%). An analogous reaction with Os3(CO)12 gives heterotetrametallic (η5-C5Me5)Re(NO)(PPh3)(C⋮CC(OMe))Os3(CO)11 (4, 87%). NMR, IR, and crystallographic data (4) show substantial contributions by +ReCCC(OMe)−M- resonance forms. Reaction of 3 and excess BF3 gas in toluene precipitates [(η5-C5Me5)Re(NO)(PPh3)(μ-η1:η3:η1-CCC)(Re(CO)4)Re(CO)5]+BF4- (5, 64%). A crystal structure shows a slightly bent C3 moiety (152(4)°) that binds a rhenium on each end and spans a third. NMR, IR, and bond length data show that 5 is best viewed as a completely metalated π propargyl or PReCC⋮C−Re(CO)5 adduct of Re(CO)4. It is likely derived by initial methoxide abstraction from 3 to give a ReCCCReRe species, followed by rearrangement. Reaction of (η5-C5Me5)Re(NO)(PPh3)(C⋮CC⋮CLi) with Re2(CO)10 and then Me3O+BF4- gives the C5OMe complex cis-(η5-C5Me5)Re(NO)(PPh3)(C⋮CC⋮CC(OMe))Re(CO)4Re(CO)5 (8, 44%). When 4 or 8 are treated with BF3 gas, Cx complexes are not detected.