The regioselective formation of (E)-β-vinylstannanes has been a long-standing challenge in transition-metal-catalyzed alkyne hydrostannation. Herein, we report a well-defined molybdenum-based system featuring two encumbering m-terphenyl isocyanides that reliably and efficiently delivers (E)-β-vinylstannanes from a range of terminal and internal alkynes with high regioselectivity. The system is particularly effective for aryl alkynes and can discriminate between alkyl chains of low steric hindrance in unsymmetrically substituted dialkyl alkynes. Catalytic hydrostannation with this system is also characterized by an electronic effect that leads to a decrease in regioselectivity when electron-withdrawing groups are present on the alkyne substrate.

Relative to other cyclic poly‐phosphorus species (that is, cyclo‐Pn), the planar cyclo‐P4 group is unique in its requirement of two additional electrons to achieve aromaticity. These electrons are supplied from one or more metal centers. However, the degree of charge transfer is dependent on the nature of the metal fragment. Unique examples of dianionic mononuclear η4‐P4 complexes are presented that can be viewed as the simple coordination of the [cyclo‐P4]2− dianion to a neutral metal fragment. Treatment of the neutral, molybdenum cyclo‐P4 complexes Mo(η4‐P4)I2(CO)(CNArDipp2)2 and Mo(η4‐P4)(CO)2(CNArDipp2)2 with KC8 produces the dianionic, three‐legged piano stool complexes, [Mo(η4‐P4)(CO)(CNArDipp2)2]2− and [Mo(η4‐P4)(CO)2(CNArDipp2)]2−, respectively. Structural, spectroscopic, and computational studies reveal a similarity to the classic η6‐benzene complex (η6‐C6H6)Mo(CO)3 regarding the metal‐center valence state and electronic population of the planar‐cyclic ligand π system.

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This is the author manuscript accepted for publication and has undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record.

This is the author manuscript accepted for publication and has undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record.