Syntheses, Structures, and Dynamic Properties of Dicobalt π Complexes of Diplatinum Polyynediyl Complexes

Reactions of Co2(CO)6(μ-Ph2PCH2PPh2) and polyynediyl complexes trans,trans-(C6F5)(p-tol3P)2Pt(CC)mPt)(Pp-tol3)2(C6F5) (PtC2mPt) are conducted in refluxing toluene. With PtC8Pt, a 1:1 adduct, trans,trans-(C6F5)(p-tol3P)2PtCCC2[Co2(CO)4(μ-PPh2CH2PPh2)](CC)2Pt(Pp-tol3)2(C6F5) (1), is isolated in 53% yield after silica gel chromatography and crystallographically characterized. The dicobalt moiety binds to a PtCCCC linkage remote from the bulky platinum endgroups, with the P−Pt−P axis of the (p-tol3P)2PtCCC(Co)2 moiety nearly parallel to the cobalt−cobalt bond and that of the (p-tol3P)2PPtCCCCC(Co)2 moiety roughly perpendicular. The 31P and 1H NMR spectra of 1 evidence dynamic behavior. At the low-temperature limit, three 31P signals are observed (2:1:1), corresponding to the p-tol3P ligands on one endgroup and those that have cis/trans relationships to the cobalt−cobalt bond on the other. Low-temperature 31P and 1H NMR spectra show multiple Ph2PCH2PPh2 signals, which are analyzed. In the case of PtC12Pt, a 2:1 adduct is the major isolable product (12%). NMR data show that the dicobalt moieties bind to the central CC linkages furthest from the endgroups. In the case of PtC16Pt, mass spectra show that 2:1 adducts can form, but 31P NMR spectra are not homogeneous, suggesting mixtures of isomers differing in the dicobalt positions.