Electrochemical Investigation of Low-Valent Multiply MM Bonded Group VI Dimers: A Standard Chemical Reduction Leads to an Unexpected Product

The synthesis and investigation of
multimetallic complexes bearing metal–metal bonds have been
significantly advanced over the last 30 years with exciting applications
across many fields. While the outlook for synthetically innovative
metal–metal species is promising, the reactivity of the classic
M2X6 alkyl dimers (where M = W, Mo; X = CH2CMe3, CH2SiMe3) is still
not fully understood. In particular, the redox characteristics of
these complexes have not been explored by cyclic voltammetry (CV).
Herein, W2(CH2CMe3)6 and
Mo2(CH2CMe3)6 (1 and 2, respectively) were characterized using CV to
show differing electrochemical behavior between the two species. Stoichiometric
reactions, guided by the results of the CV experiments, led to the
isolation of an alkylidyne-bridged dimer bearing a rare structural
motif, W2(μ-CCMe3)2(CH2CMe3)4 (3). Single-crystal
X-ray diffraction (SCXRD) and 1H and 13C nuclear
magnetic resonance spectroscopy (NMR) were used to establish the connectivity
of the structure in the solid and solution phases. Density functional
theory (DFT) calculations on 1–3 and
the previously reported W2(CSiMe3)2(CH2SiMe3)4 (4) were
used to rationalize the reactivity of 1 to form 3 and the structural differences between 3 and 4. Complexes 3 and 4 constitute
a case in which the stereoelectronic properties of the silyl neopentyl
ligand can affect differences in structure and bonding.