η2-Bonded methylenecyclopropane complexes of rhodium(I), iridium(I), platinum(0), and platinum(II): crystal and molecular structure of acetylacetonatobis(η2-methylenecyclopropane)rhodium(I)

Abstract

Reactions of methylenecyclopropane (1), trans-2,3-dimethoxycarbonylmethylenecyclopropane (2), or cis-2,3-dimethoxycarbonylmethylenecyclopropane (3) with the appropriate η²-ethylene–metal complexes yield [Rh(un)₂-(acac)]{un =(1)–(3)}, [{Rh(un)₂Cl}₂]{un =(2) or (3)}. [Rh(un)₂(η⁵-C₅H₅)][un =(2)], [lr(un)₂(acac)]{un =(2) or (3)}. [Pt(un)(PPh₃)₂]{un =(1)–(3)}, and trans-[PtCl₂(un)(C₅H₅N)]{un =(2) or (3)}. The complexes [Rh(un)(CO)L]{un =(2); L = acac or η⁵-C₅H₅} are described. ¹H, ¹³C, and ³¹P N.m.r. data are reported and discussed, and the complex [Fe(un)(CO)₄]{un =(3)} is shown to be stereochemically rigid at ambient temperature. An X-ray crystallographic determination of acetylacetonatobis(η²-methylenecyclopropane)rhodium(I)(4a) establishes that the rhodium atom is in a square-planar configuration with two adjacent sites occupied by the acetylacetonate ligand. The methylenecyclopropane ligands are bonded with the exocyclic double-bond approximately perpendicular to the co-ordination plane of the rhodium atom and in converse orientation to one another. The plane of the cyclopropane ring lies normal to the valence direction of the rhodium–olefin bond.