Synthesis and redox chemistry of cycloheptatrienyl molybdenum carbon-chain complexes featuring diimine support ligands: [Mo{(C≡C)nC≡ CR}(R′N=CH-CH=NR′)(η-C7H7)], (n = 0 or 1)

The alkynyl complexes [Mo(C≡CR)(R′-dab)(η-C 7H7)] (dab = diazabutadiene; R′ = tBu, R = Ph, 2a; C6H4-4-Me, 3a; tBu, 4a; R′ = C6H4-4-Me, R = Ph, 2b) have been synthesised by reaction of [MoBr(R′-dab)(η-C7H7)] with LiC≡CR in thf. Crystallographic characterisation of [Mo(C≡CC6H 4-4-Me)(tBu-dab)(η-C7H7)], 3a determines a Mo-Cα bond distance of 2.154(3) Å. Cyclic voltammetric investigations on the alkynyl complexes 2a, 2b, 3a, 4a and the extended chain butadiynyl derivative [Mo(C≡CC≡CSiMe 3)(tBu-dab)(η-C7H7)], 5a, reveal that each complex exhibits a chemically and electrochemically reversible one-electron oxidation to give the corresponding 17-electron radical cation. Characterisation of the radicals [2a]+, [2b]+, [3a] +, and [5a]+ by IR and EPR spectroscopic techniques indicates that the redox process is strongly metal centred. Spectroscopic and synthetic investigations establish that 17-electron radicals of the type [Mo{(C≡C)nC≡CR)}(R′-dab)(η-C7H 7)]+ (n = 0 or 1) have relatively low thermodynamic stability. © 2013 Elsevier B.V. All rights reserved.