Heteroleptic Chini-Type Platinum Clusters: Synthesis and Characterization of Bis-Phospine Derivatives of [Pt_3<i>n</i>(CO)_6<i>n</i>]^2–(<i>n</i>= 2–4)

Abstract

The reactions of [Pt 3 n (CO) 6 n ] 2– ( n = 2–4) homoleptic Chini-type clusters with stoichiometric amounts of Ph 2 PCH 2 CH 2 PPh 2 (dppe) result in the heteroleptic Chini-type clusters [Pt 6 (CO) 10 (dppe)] 2–, [Pt 9 (CO) 16 (dppe)] 2–, and [Pt 12 (CO) 20 (dppe) 2 ] 2– . Their formation is accompanied by slight amounts of neutral species such as Pt 4 (CO) 4 (dppe) 2, Pt 6 (CO) 6 (dppe) 3, and Pt(dppe) 2 . A similar behavior was observed with the chiral ligand R-Ph 2 PCH(Me)CH 2 PPh 2 (R-dppp), and two isomers of [Pt 9 (CO) 16 (R-dppp)] 2– were identified. All the new species were spectroscopically characterized by means of IR and 31 P NMR, and their structures were determined by single-crystal X-ray diffraction. The results obtained are compared to those previously reported for monodentate phosphines, that is, PPh 3, as well as more rigid bidentate ligands, that is, CH 2 ═C(PPh 2 ) 2 (P^P), CH 2 (PPh 2 ) 2 (dppm), and o -C 6 H 4 (PPh 2 ) 2 (dppb). From a structural point of view, functionalization of anionic platinum Chini clusters preserves their triangular Pt 3 units, whereas the overall trigonal prismatic structures present in the homoleptic clusters are readily deformed and transformed upon functionalization. Such transformations may be just local deformations, as found in [Pt 9 (CO) 16 (dppe)] 2–, [Pt 9 (CO) 16 (R-dppp)] 2–, [Pt 12 (CO) 22 (PPh 3 ) 2 ] 2–, and [Pt 9 (CO) 16 (PPh 3 ) 2 ] 2–; an inversion of the cage from trigonal prismatic to octahedral, as observed in [Pt 6 (CO) 10 (dppe)] 2– and [Pt 6 (CO) 10 (PPh 3 ) 2 ] 2–; the reciprocal rotation of two trigonal prismatic units with the loss of a Pt–Pt contact as found in [Pt 12 (CO) 20 (dppe) 2 ] 2– .