A Comparison of Phosphaferrocene and Phospharuthenocene Ligands in Rh⁺‐Catalysed Enamide Hydrogenation Reactions: Superior Performance of the Phospharuthenocene

Abstract

Enantiopure Cp*-substituted 3,4-dimethyl-5-phenylphosphametallocene-2-methanols (M=Fe, Ru) have been prepared from the corresponding 2-carboxy-(-)-menthylphospholide anion and elaborated into 2-CH(2)PPh(2) phosphametallocenes (13: M=Fe; 14: M=Ru) and 2-CH(2)PtBuR substituted phospharuthenocenes (R=tBu, Me). The crystal structures of complexes [Rh(1,5-cod)(eta(2)-L)](+)BF(4)(-) (L=13, 14) reveal significantly different aryl group configurations. Comparative studies of the hydrogenation of para-substituted N-acetylcinnamate esters with these pre-catalysts show a superior performance for the phospharuthenocene derivative in terms of both rate and enantioselectivity.

Applications of Aza‐ and Phosphaferrocenes and Related Compounds in Asymmetric Catalysis

“…More recently, a comparison of rhodium-catalyzed hydrogenations in the presence of phosphaferrocene and phospharuthenocene ligands has been provided by Carmichael and coworkers (Eq. (29)) [66]. In the case of complexes 54 and 55, the ruthenium-based ligand furnishes better rates and enantioselectivity than the iron analogue.…”

Diastereoselective synthesis and coordination chemistry of enantiopure keto-bis-(2-phosphametallocene)s

“…15 Phosphametallocenes are particularly interesting for use as ligands because they exhibit an easily exploited planar chirality 16,17 and show the kind of "modular" composition that is found in the highly successful metallocene phosphine classes; 18 they are also well proven in catalysis. [19][20][21] However, ligands whose chirality is generated uniquely by phosphametallocenes are rare [21][22][23] with only Ganter's 9 (Fig. 3) having been catalytically tested, in a Pd catalysed alkylation of 1,3-diphenylallyl acetate.…”

Preparation of Osmium η5-Phospholide Complexes and Their Reactions with Acyl Electrophiles: C═O Bond Cleavage and C−C Bond Formation within the Metal Coordination Sphere

“…Heavier homologues of the group 8 triad, however, have received little attention. Phospharuthenocenes are relatively newer entries to this field: the first mono- and diphospharuthenocenes were reported in 1994 and 2002, respectively . To the best of our knowledge, none of such complexes with an osmium core have been described to date. , …”