Metals helping metals: The bimetallic spirocyclic bridged‐carbene complex 1 reacts almost quantitatively with CO by formal “insertion” into the RhC(Li) bond to form the dimeric complex 2, the first example of a μ2,η2‐(O,C) lithium–rhodium ketene complex (see scheme). Complex 2 reacts with water to transform the ketene ligand into a methine group by CO elimination.

The Li-C-Rh, bimetallic, phosphinimine spirocyclic, bridged carbene complex 1 was readily prepared from dilithiobis(diphenylphosphoranosilylimido)methandiide, [Li 2 L] 2 , and an equimolar (Rh/Li, 1:1) amount of [Rh(cod)Cl] 2 . Subsequent reaction with a different metal precursor, in the present cases, [Pd(allyl)Cl] 2 , yielded the spirocyclic Rh-Pd heterobimetallic 2 or, if a second equivalent of [Rh(cod)Cl] 2 was used, the spirocyclic Rh-Rh homobimetallic 3 was obtained; thus the system presents an effective synthetic route for the preparation of homo-or heterobimetallic complexes. All of the complexes have constrained symmetry, which creates in some cases isomeric and enantiomeric structures. The Li-Rh complex 1 thermally rearranged to the chelated, orthometalated, Rh complex 6, wherein the Rh(I) center is bound to the ipso carbon of a phenyl ring and a methine carbon formed from protonation of the spiro carbon. Remarkably, controlled hydrolysis of 6 reversed the orthometalation and provided an iminophosphorane-methine chelate complex of Rh(I), 7. Reactions of the cod-substituted complexes 2, 3, and 7 with CO resulted in the replacement of cod substituents to form parallel Rh carbonyl complexes (4, 5, and 8). The allyl substituents in the system were not affected. The carbonyl complexes 5 and 8 could be made independently from [Rh(CO) 2 Cl] 2 and either the dilithium methandiide or the methine form of the ligand as appropriate. Complexes 2-7 have been structurally characterized herein. Complexes 3 and 5 are chiral (because they lack rotation-reflection axes), but the products here are unresolved racemic mixtures according their NMR spectra. The complex 2 and its derivative 4 exist as unequal diastereomeric pairs according to the NMR. Fluxional NMR behavior is observed for 1, wherein the cod appears to partly dissociate and invert, for 2 and 3 where the cod exchange appears to involve a different mechanism being assisted by dissociation of one imine substituent, for 2 and 4 wherein allyl syn-syn, anti-anti exchange occurs between the diastereomers, and for 7 wherein the coordinated and uncoordinated imine groups exchange.

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Syntheses of tetraethyl iso­cyanato­methyl­enedi­phospho­nate and the title compound, C14H37NO7P2Si4, are reported. The structure of the latter shows disorder of the isocyanate group, but bond lengths and angles within this group are normal.