Synthesis and X-ray crystal structure of [Pt2(μ-H)(μ-S)(dppe)2]+, a diplatinum cation with hydrido and sulphido ligands bridging a PtPt bond

Reaction Chemistry of Complexes Containing PtH, PtSH, or PtS Fragments: From Their Apparent Simplicity to the Maze of Reactions Underlying Their Interconversion

The relevance of platinum in the reaction of thiophene and derivatives with homogeneous transition-metal complexes as models for hydrodesulfurization has led us to the study of the reaction chemistry of complexes containing Pt--H, Pt--SH, and Pt--S fragments. Exploration of the reactions triggered by addition of controlled amounts of Na2S or NaSH to [Pt2(H)2(mu-H)(dppp)2]ClO4 (1) has provided evidence of the formation of complexes [Pt2(mu-H)(mu-S)(dppp)2]ClO4 (2), [Pt(H)(SH)(dppp)] (3), [Pt2(mu-S)2(dppp)2] (4), [Pt2(mu-S)(dppp)2] (5) and [Pt(SH)2(dppp)], in which dppp denotes 1,3-bis(diphenylphosphanyl)propane. Consequently, complexes 1, 2, and 5 as well as the already reported 3, 4, and [Pt(SH)2(dppp)] have been obtained and fully characterized spectroscopically. Also the crystal structures of 1 and 2 have been solved. Complexes 1-5 constitute the main framework of the network of reactions that account for the evolution of 1 under various experimental conditions as shown in Scheme 1. Apparently, this network has complexes 2 and 4 as dead-ends. However, their reciprocal interconversion by means of the replacement of one bridging hydride or sulfide ligand in the respective {Pt(mu-H)(mu-S)Pt} and {Pt(mu-S)2Pt} cores enables the closure of the reaction cycle involving complexes 1-5. Theoretical calculations support the existence of the undetected intermediates proposed for conversion from 1 to 2 and from 3 to 2 and also account for the fluxional behavior of 1 in solution. The intermediates proposed are consistent with the experimental results obtained in comparable reactions carried out with labeled reagents, which have provided evidence that complex 1 is the source of the hydride ligands in complexes 2 and 3. Overall, our results show the strong dependence on the experimental conditions for the formation of complexes 1-5 as well as for their further conversion in solution.

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

When the ortho-metallated complexes cis-[Pt(kappa(2)-C6H3-5-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 [Pt2(kappa(2)-C6H3-5-R-2-PPh2)2(mu-C6H3-5-R-2-PPh2)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) A. 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(kappa(2)-C6H3-6-Me-2-PPh2)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)(kappa(1)-C-C6H3-6-Me-2-PPh2)(2-C6H3-6-Me-2-PPh2)] 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(PPh3)2L] (L = PPh3, C2H4) gives diplatinum(I) complexes [Pt2(mu-C6H3-5-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) A. There is no evidence for the formation of an analogue containing mu-C6H3-6-Me-2-PPh2. The axial PPh3 ligands of 16 are readily replaced by ButNC giving [Pt2(mu-2-C6H4PPh2)2(CNBut)2] 18, which is protonated by HBF4 to form a mu-hydridodiplatinum(II) salt [Pt2(mu-H)(mu-2-C6H4PPh2)2(CNBut)2]BF4 [21]BF4. The J(PtPt) values in [21]BF4 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(mu-Z)(mu-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) A and a Pt-H bond length of 1.62(1) A, 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.