Diphosphine-Substituted Rhodium Carbonyl Clusters: Synthesis and Structural and Spectroscopic Characterization of the Heteroleptic Rh4(CO)8+2n(L)2−n (n = 0, 1) and {Rh4(CO)10L}2 Monomeric and Dimeric Species

Tetranuclear rhodium carbonyl clusters are vital catalytic precursors; yet derivatives featuring bidentate phosphines are less common, due to the propensity for cluster fragmentation during synthesis. This study reports the successful isolation of five new heteroleptic species by reacting Rh4(CO)12 with various bidentate diphosphines under homogeneous conditions and at room temperature, namely the mono-substituted Rh4(CO)10(dppe) (1) and Rh4(CO)10(dppb) (3), the rare bis-substituted derivative Rh4(CO)8(dppe)2 (2), and the two unique dimeric assemblies {Rh4(CO)10(dpp-hexane)}2 (4) and {Rh4(CO)10(trans-dppe)}2 (5). The tetrahedral Rh4 core of the cluster precursor was preserved in all cases. The new compounds were characterized via infrared (IR) spectroscopy and single-crystal X-ray diffraction (SC-XRD). Furthermore, variable-temperature (VT) 31P{1H} NMR spectroscopy elucidated the dynamic behavior of the phosphorus atoms. This work reports a robust methodology for accessing stable, low-nuclearity rhodium phosphine clusters with tunable properties.