The bis-2,5-diphenylphosphole xantphos ligand (XDPP) 1 reacts with the [AuCl(tht)] complex to afford the monocoordinated [Au(XDPP)Cl] 2 and the dicoordinated chelate species [Au(XDPP)Cl] 3. Addition of AgOTf on this mixture, at room temperature, affords the cationic [Au(XDPP)][OTf] complex 4 which was fully characterized. An X-ray crystal structure analysis confirms the bent structure of this 14 VE [ML(2)](+) complex. Reaction of 4 with HSiMe(2)Ph in tetrahydrofuran at -78 degrees C yields the dinuclear [(XDPP)Au-H-Au(XDPP)](+) cationic complex 5, in which the hydride bridges the two [Au(XDPP)](+) metal fragments. In 5, the Au-P bond lengths are different and the phosphorus atoms which are located nearly trans to the hydride ligand exhibit significantly shorter P-Au bond lengths. Reaction of 4 with DSiMe(2)Ph to form the [(XDPP)Au-D-Au(XDPP)](+) complex 6 allowed to unambiguously ascribe the chemical shift of the deuteride in (2)H NMR (delta = 7.0 ppm with a (2)J(DP) = 8.4 Hz. The electronic structure of the [(XDPP)Au-H-Au(XDPP)](+) complex was studied through density functional theory calculations. An orbital analysis is developed in which complex 5 is viewed as the combination of two 12 electrons fragments [Au(XDPP)](+) with H(-). This analysis reveals that the hydride interacts in a bonding way with the sigma MO between the two gold atoms and in an antibonding way with a combination of d orbitals at the metal centers. This simple description allows to rationalize the inequivalence of the two types of P-Au bonds in 5.

Two new xanthene-phosphole derivatives, 3 and 4, were synthesized through the nucleophilic substitution of the cyano group in 1-P-cyano-2,5-diphenylphosphole (1) and 1-P-cyano-3,4-dimethylphosphole (2) by the 4,5-dilithium salt of 9,9‘-dimethylxanthene. For this, a new synthetic procedure was developed, allowing the synthesis of the required 1-P-cyano-2,5-diphenylphosphole from the 1,2,5-triphenylphosphole. Both ligands (DPP-Xantphos 3 for the diphenyl derivative and DMP-Xantphos 4 for the dimethyl derivative) react with [Pd(allyl)Cl]2 to afford the corresponding cationic complexes 5Cl and 6Cl. Using AgOTf, stable triflate complexes 5OTf and 6OTf could be isolated. The chloride complexes, on the other hand, exhibit a limited stability in solution. The DPP-Xantphos derivative 5Cl eliminates allyl chloride to yield the dimeric palladium(0) complex 7 of general formula [Pd(3)]2, in which each palladium is coordinated to the two phosphorus atoms of the same ligand and to one double bond of one phosphole unit of the second ligand. Decomposition of complex 6Cl furnished a mixture of compounds featuring a dimeric trinuclear species of general formula [Pd3(4)2Cl2]. This complex was also synthesized directly. Reaction of the DMP-Xantphos ligand 4 with 1 equiv of [Pd(COD)Cl2] and 2 equiv of [Pd(dba)2] afforded dimer 8, which features one 18-VE Pd0 center and two Pd-Cl fragments, which are coordinated to the dienic system of the two phosphole ligands and connected through a single Pd−Pd bond. The catalytic activity of the triflate complexes 5OTf and 6OTf was evaluated in the allylation of aniline. Whereas the DMP-Xantphos derivative 6OTf exhibited a poor catalytic activity, very good conversion yields were obtained with the DPP-Xantphos complex 5OTf. On the basis of X-ray structure data and DFT calculations, it was concluded that the high catalytic activity of the DPP-Xantphos derivative complex [Pd(allyl)3][OTf] (6OTf) results from the combination of two effects:  a large P−Pd−P bite angle, which enhances the reactivity of the allyl ligand, and the strong π-accepting capacity of the diphenylphosphole moiety, which allows the easy formation of a 14-VE complex.