Cooperativity in Transition Metal Tetrylene Complexes

Abstract

Cooperative reactivity between transition metals and ligands, or between two metals, has created significant opportunities for the development of new transformations that would be difficult to carry out with a single metal. Here we explore cooperativity between transition metals and divalent heavier group 14 elements (tetrylenes), a less-explored facet of the field of cooperativity. Tetrylenes combine their strong σ-donor properties with an empty p-orbital that can accept electron density. This ambiphilicity has allowed them to form metal tetrylene and metallotetrylene complexes that place a reactive site adjacent to the metal. We have selected examples to demonstrate what has been achieved so far regarding cooperative reactivity, as this already spans metal-, tetrylene- or multi-site-centred bond cleavage, cycloaddition, migration, metathesis, and insertion. We also highlight some challenges that need to be overcome for this cooperativity to make it to catalysis.

Keywords: Cooperative effects; Group 14 elements; Main group elements; Multi-site activation; Tetrylenes.

Figure 1

General scheme for metal tetrylenes and metallotetrylenes, early examples, and the cooperative bond activation that could be envisioned between the two centres.

Scheme 1

Cleavage of dihydrogen at group 10 metal germylenes.

Scheme 2

Activation of H−H and B−H bonds at a zero‐valent nickel silylene. L=N(SiMe₃)(Dipp); Dipp=2,6‐ ⁱ Pr₂C₆H₃.

Scheme 3

Cleavage of strong bonds at the Ge(II) centre of metallogermylene 9. Ar=2,6‐ ⁱ Pr‐C₆H₃, BAr^F=tetrakis[3,5‐bis(trifluoromethyl)phenyl]borate.

Scheme 4

Multi‐site oxidative addition across a metal tetrylene bond. Trip=2,4,6‐ ⁱ Pr₃‐C₆H₂.

Scheme 5

Metallogermylene containing electropositive Zn. Ar=2,6‐ ⁱ Pr‐C₆H₃.

Scheme 6

Oxidative addition at a bimetallic Rh−Ir complex.

Scheme 7

Cycloaddition reactivity of 1.

Scheme 8

Stannylene to metallostannylene transformations through 1,2‐migration. Os L=P ⁱ Pr₃; Ru L=1,3‐bis(2,6‐dimethylphenyl)imidazol‐2‐ylidene.

Scheme 9

Reversible 1,2‐aryl migration and synthesis of silabenzyl intermediates.

Scheme 10

Reversible metathesis at Ge(II) without direct involvement of the transition metal R=Ph, ⁱ Pr.

Scheme 11

Glaser‐Tilley mechanism for alkene hydrosilylation.

Scheme 12

Ethylene insertion at Mn silylene hydride complexes.

Scheme 13

Schrock‐type titanium silylenes in [2+2] cycloadditions.

Scheme 14

Reactions of unsaturated compounds with a low‐valent nickel silylene.

Scheme 15

Reactivity of metal hydrido(hydrosilylenes) towards carbonyl compounds and nitriles.

Scheme 16

Reactivity of pincer silylene complexes towards simple ketones.

Scheme 17

Cycloaddition reactions at ruthenium silylenes.

Scheme 18

Isocyanate reactivity at ruthenium hydrido silylenes.

Scheme 19

Divergent reactivity of Ru and W tetrylenes towards isothiocyanate.

Scheme 20

Bimetallic reduction of CO₂ at a cobalt silylene complex.

Scheme 21

Reactivity of heteroallenes at a manganese silylene.

Scheme 22

Reaction of a nickel(0) silylene with N₂O to form a Ni(II) iminosilane via a rare metal‐stabilised silanone intermediate.