Functionalization of 1,3-diphosphacyclobutadiene cobalt complexes via Si–P bond insertion

Abstract

AbstractWe report the synthesis of functionalized 1,3-bis(diphosphacyclobutadiene) complexes via the insertion of carbon-oxygen bonds of ethers, esters, aldehydes and amides into the P–Si bond of silylated complexes. Reactions of [K(tol)2][Co(η4-P2C2R2)2] [[K(tol)2][1a]:R=tBu,[K(tol)2][1b]:R=tPent (=tert-pentyl)] with Me3SiCl afford the trimethylsilyl-substituted derivatives [Co(η4-P2C2R2SiMe3)(η4-P2C2R2)] (2a,b, R=tBu,tPent). The Me3Si group is connected to a phosphorus atom of one of the 1,3-diphosphacyclobutadiene ligands.2a,breadily react with organic substrates containing C–O single and C=O double bonds at ambient temperature. [Co(η4-P2C2R2(CH2)4OSiMe3)(η4-P2C2R2)] (3a,b) are formed by reaction of2a,bwith traces of THF. They can also be isolated by reacting the THF solvates [K(thf)2{Co(P2C2tBu2)2}] ([K(thf)2][1a]) and [K(thf)3{Co(P2C2tPent2)2}] ([K(thf)3][1b]) with Me3SiCl in toluene or THF. The adamantyl-substituted complex [Co(η4-P2C2Ad2(CH2)4OSiMe3)(η4-P2C2Ad2)] (3c) was prepared analogously from [K(thf)4{Co(P2C2Ad2)2}] and Me3SiCl.[K(thf)2][1a]reacts cleanly with Ph3SnCl affording [Co(η4-P2C2tBu2SnPh3)(η4-P2C2tBu2)] (4) in high yield. Reaction of2awith styrene oxide affords [Co(η4-P2C2tBu2PhC2H3OSiMe3)(η4-P2C2tBu2)] (5) as a single regioisomer. By contrast, multinuclear NMR spectroscopic studies indicate mixtures of two isomeric insertion products6/6′ and7/7′, respectively, which result from the insertion of 1,2-epoxy-2-methylpropane and 1,2-epoxyoctane. Moreover, these monitoring studies show that reactions of2awith acyclic ethers afford alkyl substituted complexes such as [Co(η4-P2C2tBu2Et)(η4-P2C2tBu2)] (8) and alkylsilyl ethers. Reaction of2awithγ-butyrolactone gives [Co(η4-P2C2tBu2(CH2)3C(O)OSiMe3)(η4-P2C2tBu2)] (9) via cleavage of the endocyclic C–O single bond of the lactone. Benzaldehyde and acetone cleanly react with2ato [Co(η4-P2C2tBu2CH(Ph)OSiMe3)(η4-P2C2tBu2)] (10) and [Co(η4-P2C2tBu2CMe2OSiMe3)(η4-P2C2tBu2)] (11), while the sterically more demanding ketones 3-pentanone and acetophenone selectively yield the known hydride complex [Co(η4-P2C2tBu2)2H] (A). Phenyl isocyanate reacts with2aat elevated temperature to form [Co(η3-P2C2tBu2CON(Ph)SiMe3)(η4-P2C2tBu2)] (12) with a functionalizedη3-coordinated ligand.[K(tol)2][1a],[K(tol)2][1b],2a,2b,3a–c,4,5, and9–12were isolated and characterized by multinuclear NMR spectroscopy, UV/Vis spectroscopy and elemental analysis.[K(tol)2][1b],2a,2b,3c,4,5, and9–12were additionally characterized by X-ray crystallography.