Ortho-Metallated complexes of platinum(ii) and diplatinum(i) containing the carbanions (2-diphenylphosphino)phenyl and (2-diphenylphosphino)-n-tolyl (n = 5, 6)

Martin A. Bennett*, Suresh K. Bhargava, Johannes Messelhäuser, Steven H. Privér, Lee L. Welling, Anthony C. Willis

*Corresponding author for this work

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    18 Citations (Scopus)


    When the ortho-metallated complexes cis-[Pt(κ2-C 6H3-5-R-2-PPh2)2] (R = H 1, Me 2) are either heated in toluene or treated with CO at room temperature, one of the four-membered chelate rings is opened irreversibly to give dinuclear isomers [Pt22-C6H3-5-R-2-PPh 2)2(-C6H3-5-R-2-PPh 2)2] (R = H 10, Me 11). A single-crystal X-ray diffraction study shows the Pt⋯Pt separation in 10 to be 3.3875(4) Å. By-products of the reactions of 1 and 2 with CO are polymeric isomers (R = H 13, Me 14) in which one of the P-C ligands is believed to bridge adjacent platinum atoms intermolecularly. In contrast to the behaviour of 1 and 2, when cis-[Pt(κ2-C6H3-6-Me-2-PPh 2)2] (cis-3) is heated in toluene, the main product is trans-3, and reaction of cis-3 with CO gives a carbonyl complex [Pt(CO)(κ1-C-C6H3-6-Me-2-PPh 2)(κ2-C6H3-6-Me-2-PPh 2)] 15, in which one of the carbanions is coordinated only through the carbon. Formation of a dimer analogous to 10 or 11 is sterically hindered by the 6-methyl substituent. Comproportionation of 1 or 2 with [Pt(PPh 3)2L] (L = PPh3, C2H4) gives diplatinum(i) complexes [Pt2(-C6H 3-5-R-2-PPh2)2(PPh3)2] (R = H 16, Me 17). An X-ray diffraction study shows that 17 contains a pair of planar-coordinated metal atoms separated by 2.61762(16) Å. There is no evidence for the formation of an analogue containing -C6H 3-6-Me-2-PPh2. The axial PPh3 ligands of 16 are readily replaced by ButNC giving [Pt2(-2-C 6H4PPh2)2(CNBut) 2] 18, which is protonated by HBF4 to form a -hydridodiplatinum(ii) salt [Pt2(-H)(-2-C6H 4PPh2)2(CNBut)2]BF 4 [21]BF4. The JPtPt values in [21]BF 4 and 18, 2700 Hz and 4421 Hz, respectively, reflect the weakening of the Pt-Pt interaction caused by protonation. Similarly, 16 and 17 react with the electrophiles iodine and strong acids to give salts of general formula [Pt2(-Z)(-C6H3-5-R-2-PPh2) 2(PPh3)2]Y (Y = Z = I, R = H 19+, Me 20+; Z = H, Y = BF4, PF6, OTf, R = H 22 +; Z = H, Y = PF6, R = Me 23+). A single-crystal X-ray diffraction study of [23]PF6 shows that the cation has an approximately A-frame geometry, with a Pt⋯Pt separation of 2.7888(3) Å and a Pt-H bond length of 1.62(1) Å, and that the 5-methyl substituents have undergone partial exchange with the 4-hydrogen atoms of the PPh2 groups of the bridging carbanion. The latter observation indicates that the added proton of [23]+ undergoes a reversible reductive elimination-oxidative addition sequence with the Pt-C(aryl) bonds.

    Original languageEnglish
    Pages (from-to)3158-3169
    Number of pages12
    JournalDalton Transactions
    Issue number29
    Publication statusPublished - 2007


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