A series of sterically tuned chelating bisarylphosphonite ligands with a cis-1,2-(bi)cycloalkane spacer and cyclic phosphonite moieties was synthesized. The spacer as well as the phosphacycles were modified to investigate their influence in the nickel-catalyzed hydrocyanation of styrene and 1,3-butadiene and the isomerization of 2-methyl-3-butenenitrile. NMR studies detect only catalytically active (P ∩ P)Ni(COD) species and no hints of the formation of catalytically inactive dibisphosphonite complexes (P ∩ P) 2 Ni are found. In the hydrocyanation of styrene, these catalysts are highly active (93% conversion) and highly regioselective (99.9% iso) at moderate catalyst concentrations (1 mol %). They also proved to be very active in the hydrocyanation of butadiene with turnover numbers of 644 and turnover frequencies of 426 h -1 at low catalyst concentrations (0.1 mol %). Moreover, they very efficiently catalyze the isomerization of 2-methyl-3-butenenitrile to the linear 3-pentenenitrile.

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Protonation (CF3SO3H) of WH2CI2L4 (L = PMe2Ph) below -70 °C in CD2CI2 gives A as the kinetic product. This shows two hydride signals at -85 °C, and inequivalent (A2M2) 31P nuclei. By -70 °C, the kinetic product converts completely to the thermodynamic product WVI(H)3Cl2L,4+, B, which has fluxional hydrides but inequivalent (A2M2) 31P nuclei. The W-P coupling constants, the W/H T\ value of B, and the green color of A support metal oxidation state IV for A and VI for B. By -30 °C, B reacts further to dissociate one phosphine, to produce stereochemically-rigid, C3-symmetric WVI(H)3Cl2L3+, C. Both the and 31P NMR spectral patterns and the W-P coupling constant support the claimed oxidation state of W(VI) in C. Above 10 °C, C decomposes both in solution (CH2CI2 or toluene) and also as a pure solid to a variety of uncharacterized products. Comparison to the result of protonation of W(H)2XYL4 (XY = Br2, L•, C1I, CIBr) support certain structural proposals for A-C and indicate how the diminished X-W -donation by the heavier halides influences these oxidative and phosphine dissociation processes.

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