The nucleophilicity of the [Pt(2)S(2)] core in [[Ph(2)P(CH(2))(n)PPh(2)]Pt(mu-S)(2)Pt[Ph(2)P(CH(2))(n)PPh(2)]] (n = 3, dppp (1); n = 2, dppe (2)) metalloligands toward the CH(2)Cl(2) solvent has been thoroughly studied. Complex 1, which has been obtained and characterized by X-ray diffraction, is structurally related to 2 and consists of dinuclear molecules with a hinged [Pt(2)S(2)] central ring. The reaction of 1 and 2 with CH(2)Cl(2) has been followed by means of (31)P, (1)H, and (13)C NMR, electrospray ionization mass spectrometry, and X-ray data. Although both reactions proceed at different rates, the first steps are common and lead to a mixture of the corresponding mononuclear complexes [Pt[Ph(2)P(CH(2))(n)PPh(2)](S(2)CH(2))], n = 3 (7), 2 (8), and [Pt[Ph(2)P(CH(2))(n)PPh(2)]Cl(2)], n = 3 (9), 2 (10). Theoretical calculations give support to the proposed pathway for the disintegration process of the [Pt(2)S(2)] ring. Only in the case of 1, the reaction proceeds further yielding [Pt(2)(dppp)(2)[mu-(SCH(2)SCH(2)S)-S,S']]Cl(2) (11). To confirm the sequence of the reactions leading from 1 and 2 to the final products 9 and 11 or 8 and 10, respectively, complexes 7, 8, and 11 have been synthesized and structurally characterized. Additional experiments have allowed elucidation of the reaction mechanism involved from 7 to 11, and thus, the origin of the CH(2) groups that participate in the expansion of the (SCH(2)S)(2-) ligand in 7 to afford the bridging (SCH(2)SCH(2)S)(2-) ligand in 11 has been established. The X-ray structure of 11 is totally unprecedented and consists of a hinged [(dppp)Pt(mu-S)(2)Pt(dppp)] core capped by a CH(2)SCH(2) fragment.

Given the nucleophilicity of the [Pt(2)S(2)] ring, the evolution of [Pt(2)(mu-S)(2)(P intersection P)(2)] (P intersection P=1,2-bis(diphenylphosphino)ethane (dppe), 1,3-bis(diphenylphosphino)propane (dppp)) metalloligands in the presence of the simplest electrophilic species, the proton, has been studied. Combined use of experimental and theoretical data has allowed the whole set of reactions ensuing the protonation of the [Pt(2)S(2)] core to be established. The titration of [Pt(2)(mu-S)(2)(P intersection P)(2)] with HCl or HClO(4) was monitored mainly by (31)P[(1)H] NMR and mass techniques. Characterization of all the species involved was completed with the determination of the crystal structure of [Pt(SH)(2)(P intersection P)], for dppe and dppp, and [Pt(3)(mu(3)-S)(2)(dppp)(3)](PF(6))(2). The first protonation step of the [Pt(2)S(2)] core leads to the stable [Pt(2)(mu-S)(mu-SH)(P intersection P)(2)](+) complex, but the second step implies disintegration of the ring, thus giving rise to various mononuclear species. The subsequent evolution of some of these species allows regeneration of [Pt(2)(mu-S)(mu-SH)(P intersection P)(2)](+), evidencing the cyclic nature of this process. Whereas the reaction pathway is essentially common for both phosphine ligands, dppe and dppp, the different coordinating ability of Cl(-) or ClO(4) (-) determines the nature of the final products, [PtCl(2)(P intersection P)], [Pt(3)(mu(3)-S)(2)(P intersection P)(3)]Cl(2) or [Pt(3)(mu(3)-S)(2)(P intersection P)(3)](ClO(4))(2). DFT calculations have corroborated the thermodynamic feasibility of the reactions proposed on the basis of experimental data.

Zirconium-mediated inter- and intramolecular reductive cyclization of alkynes and diynes has been used to prepare a new class of bidentate phosphine, based on a four-carbon sp2-hybridized tether. Intermolecular coupling of diphenylacetylene and but-2-yne with Negishi's reagent followed by transmetalation with copper chloride prior to quenching with chlorodiphenylphosphine affords the corresponding acyclic diphosphines 1,4-bis(diphenylphosphino)-1,2,3,4-tetraphenyl-1,3-butadiene (2a; 1,2,3,4-Ph4-NUPHOS) and 1,4-bis(diphenylphosphino)-1,2,3,4-tetramethyl-1,3-butadiene (2b; 1,2,3,4-Me4-NUPHOS), respectively. A single-crystal X-ray analysis of the former has been obtained. Surprisingly, 1-phenylpropyne undergoes a highly regioselective reductive cyclization to afford 1,4-bis(diphenylphosphino)-1,3-diphenyl-2,4-dimethyl-1,3-butadiene (2c; 1,3-Ph2-2,4-Me2-NUPHOS). Similarly, transmetalation of the zirconacyclopentadiene generated from 3,9-dodecadiyne and 1,8-diphenyloctadiyne followed by electrophilic liberation of the resulting copper diene reagent with chlorodiphenylphosphine gave 1,2-bis(1-(diphenylphosphino)prop-1-ylidene)cyclohexane (2d; 1,4-Et2-2,3-cyclo-C6H8-NUPHOS) and 1,2-bis(1-(diphenylphosphino)benzylidene)cyclohexane (2e; 1,4-Ph2-2,3-cyclo-C6H8-NUPHOS), respectively. This methodology provides a convenient and versatile one-pot synthesis of a wide range of 1,3-diene bridged diphosphines. Single-crystal X-ray analyses of [(1,2,3,4-Ph4-NUPHOS)PdCl2], [(1,3-Ph2-2,4-Me2-NUPHOS)PdCl2], and [(1,4-Ph2-2,3-cyclo-C6H8-NUPHOS)PtCl2] reveal that these new phosphines coordinate to palladium and platinum in much the same manner as BINAP and dpbp, with a significant torsional twist about the C(2)−C(3) bond of the backbone. The copper diphosphine intermediate [Cu(1,4-Et2-2,3-cyclo-C6H8-NUPHOS)Cl]2 (1d) has also been isolated and characterized by single-crystal X-ray analysis and exists as the chloro-bridged dimer in which the 1,2-bis(1-(diphenylphosphino)prop-1-ylidene)cyclohexane coordinates in a bidentate manner. Palladium complexes of these new diphosphines are highly active for the cross-coupling of bromobenzene and sec-butylmagnesium bromide. Catalyst mixtures based on 1,2,3,4-Ph4-NUPHOS are far superior to those based on BINAP, with activities of 6900 and 260 (mol of product) (mol of palladium)-1 h-1, respectively. In fact, catalysts based on 1,2,3,4-Ph4-NUPHOS are ∼30 times more active than the most active catalyst reported to date for this coupling. In comparison, the selectivity of the corresponding cross-coupling with 2-bromopropene depends markedly on the nature of the NUPHOS derivative. In general, those based on NUPHOS derivatives with acyclic tethers, namely 2a−c, are highly selective for the formation of 2,3-dimethylpentene, while those formed from 2d,e gave a mixture of 2,3-dimethylpentene, 2-methylhexene, and 2,3-dimethylbutadiene. The initial TOF, measured after 20 min, also shows a marked variation on the nature of the phosphine and while all NUPHOS-based catalysts outperform those based on BINAP, catal...

Complexes [{Pt2(μ3-S)2(dppp)2}Pt(cod)]Cl2 (1) and [{Pt2(μ3-S)2(cod)2}Pt(dppp)]Cl2 (3), where dppp = 1,3-bis(diphenylphosphino)propane and cod = 1,5-cyclooctadiene, have been synthesized by reacting [Pt2(μ-S)2(dppp)2] and [PtCl2(cod)] (1:1), and [Pt(SH)2(dppp)] and [PtCl2(cod)] (1:2), respectively. Complex 1 has not allowed substitution of cod by the chelating dppp ligand. Remarkably, the reaction of 1 with methoxide anion yields [{Pt2(μ3-S)2(dppp)2}Pt(C8H11)]Cl (2), which entails deprotonation of cod instead of the nucleophilic attack of CH3O- on the olefinic bond. In addition, replacement of the deprotonated cod ligand in 2 by dppp has not been achieved. A combination of experimental data and DFT calculations in 2 is consistent with the binding of C8H11 - to platinum(II) by means of one η2-alkene and one η1-allyl bond. The structures of 1 and 2 have been confirmed by single-crystal X-ray diffraction. Analogous to 1, the reaction of 3 with sodium methoxide causes the subsequent deprotonation of the two cod ligands, yielding [{Pt2(μ3-S)2(cod)(C8H11)}Pt(dppp)]Cl (4) and [{Pt2(μ3-S)2(C8H11)2}Pt(dppp)] (5). In contrast to 1, replacement of cod by dppp in 3 and 4 leads to 1 and 2, respectively. Also, the substitution of one C8H11 - ligand by dppp in 5 leads to 2. On the basis of DFT calculations, with inclusion of solvent effects, the factors governing the chemical behavior of the {Pt(cod)}2+ fragment bonded to a [Pt2(μ-S)2L4] (L2 = dppp, cod, or C8H11 -) metalloligand are discussed.

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