Synthesis, Redox Chemistry,and Electronic Structure of the Butadiynyl and Hexatriynyl Complexes[Mo{(CC)nCCR}(L2)(η-C7H7)]z(n= 1, 2; z= 0, 1; R= SiMe3, H; L2= 2,2′-bipyridine, Ph2PCH2CH2PPh2)

Two series of extended carbon chain butadiynyl and hexatriynylcomplexes, [Mo{(CC)nCCSiMe3}(bpy)(η-C7H7)] (n= 1, 2; bpy = 2,2′-bipyridine) and [Mo{(CC)nCCR}(dppe)(η-C7H7)] (n= 1, R = H, SiMe3; n= 2, R = SiMe3; dppe = Ph2PCH2CH2PPh2), have been prepared and structurally characterized.The redox chemistry of these complexes has been investigated by cyclicvoltammetry, and the 17-electron radical cations resulting from one-electronoxidation have been characterized by spectroelectrochemical IR andUV–visible methods and EPR spectroscopy. DFT calculations onthe H-terminated model complexes [Mo{(CC)nCCH}(L2)(η-C7H7)]z(L2= bpy, dppe) reveala largely metal-centered HOMO (z= 0) with a modestincrease in carbon chain character with increasing chain length. Spindensity calculations for the 17-electron radical cations (z= 1) show large coefficients of spin density at the metalcenter, consistent with the remarkably high stability of the experimentalcomplexes. However, both DFT theoretical and experimental syntheticstudies highlight a distinction between the bpy- and dppe-supportedsystems. The 17-electron complexes [Mo{(CC)nCCSiMe3}(bpy)(η-C7H7)]PF6(n= 1, 2) are unique examplesof isolable, metal-stabilized butadiynyl and hexatriynyl radicals.In contrast, the dppe radical [Mo(CCCCSiMe3)(dppe)(η-C7H7)]笘扮⭬chain-centered reactivity, consistent with enhanced coefficients ofspin density at Cβand Cδin themodel complex [Mo(CCCCH)(dppe)(η-C7H7)]. [ABSTRACT FROM AUTHOR]