We recently reported the bisdecarbonylation of o-carbomethoxybenzoylpentacarbonylmanganese(I), 1, to give 2 in which the carbomethoxy group acts as a chelating ligand.' A monodecarbonylated compound could be trapped with external phosphite but could not be directly observed by spectral means. The more rapid loss of the second CO from 1 might be related to the formation of a particularly stable chelated product (Scheme I).p-Metallo-a,@-unsaturated carbonyl compounds with a chelating carbonyl group, 3, are readily formed in many diverse

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A series of spirocyclic monoorganosilicon compounds of the form RSi(OPO) 2 Cl [R = phenyl (1 1); p-tolyl (2 2); benzyl (3 3); Me (4 4); t Bu (5 5); thexyl (6 6)] (OPO = 1-oxo-2-pyridinone) was synthesized and characterized by 1 H , 13 C, and 29 Si NMR spectroscopy, X-ray crystallography, and elemental analysis. In the solid state, complexes 1 1, 2 2, and 3 3 are neutral and possess cis-OPO ligands in an octahedral arrangement, and complexes 4 4, 5 5, and 6 6 are cationic and possess effectively trans-OPO ligands in nearly ideal square pyramidal geometries along the Berry-pseudorotation coordinate. In 4-6 4-6, chloride dissociation is attributed to the additive effect of multiple intermolecular C-H•••Cl interactions in their crystals. In DMSO-d 6 solution, compounds 1 1-6 6 form cationic hexacoordinate DMSO adducts with trans-OPO ligands, all of which undergo dynamic isomerization with energy barriers of ~18-19 kcal/mol. Compounds with better leaving groups, (p-tolyl)Si(OPO) 2 X [X = I (7 7); X = triflate (8 8)], exhibit identical solution NMR spectra as 2 2, supporting anion dissociation in each. The fluoride derivatives RSi(OPO) 2 F [R = benzyl (9 9); Me (10 10)] exhibit hexacoordinate geometries with cis-OPO ligands in the solid state and exhibit dynamic isomerization in solution. Overall, these studies indicate, in both the solid and solution states, that the trans-OPO ligand arrangement is favored when anions are dissociated and a cis-OPO ligand arrangement when anions are coordinated.

Der nach Literaturmethoden dargestellte Titelkomplex (I) wird durch Pyrolyse im Vakuum decarbonyliert.