Complexing modes of the phosphole moiety

α-Cationic Phospholes: Synthesis and Applications as Ancillary Ligands

A series of structurally differentiated α‐cationic phospholes containing cyclopropenium, imidazolium, and iminium substituents has been synthesized by reaction of chlorophosphole 1 with the corresponding stable carbenes. Evaluation of the donor properties of these compounds reveals that their strong π‐acceptor character is heavily influenced by the nature of the cationic group. The coordination chemistry of these newly prepared ligands towards Au^I centers is also described and their unique electronic properties exploited in catalysis. Interestingly, α‐cationic phosphole containing catalysts were not only able to accelerate model cycloisomerization reactions, but also to efficiently discriminate between concurrent reaction pathways, avoiding the formation of undesired product mixtures.

Phosphole-based ligands in catalysis

This review provides an overview of phosphole-based ligand families (monophospholes, multidentate hybrid phosphole ligands, diphosphole and 2,2′-biphosphole-based ligands) and their potential in metal- and organo-catalyzed reactions (asymmetric reactions included).

Reactions of Bis(triphenylphosphonio)isophosphindolide Salts with Mercury(II) Compounds: Coordination Induced Addition and Oxidation Reactions and Synthesis of a Monomeric 1:1 Complex of the Type [R(2)(R'O)P]HgBr(2)

Bis(triphenylphosphonio)isophosphindolide triflate (1[CF(3)SO(3)]) reacted with HgCl(2) and H(2)O or MeOH to give a phosphinito complex which was converted with excess HgCl(2) into the dimercury complex 5. In contrast, methanolysis of 1[X] (X = CF(3)SO(3), Br) in the presence of Hg(OAc)(2) afforded the phosphonium cation 9. A mercury complex 8 was isolated for X = Br as a reaction intermediate. Salts of a macrocyclic cation with a constitution similar to that of 9 were obtained by reaction of 1[CF(3)SO(3)] with Hg(OAc)(2) and triethylene glycol. The products were characterised by (1)H, (13)C, and (31)P NMR spectroscopy; in addition, (199)Hg NMR data of some complexes were obtained from 2D (31)P,(199)Hg shift correlations. Complexes 5 (space group P2(1)2(1)2(1), Z = 4, a = 12.449(2) Å, b = 17.583(3) Å, c = 23.111(3) Å, V = 5058.8(14) Å(3), 8917 reflections refined to R(w2) = 0.103) and 8 (space group C2/c, Z = 8, a = 20.028(2) Å, b = 15.513(2) Å, c = 30.247(8) Å, beta = 91.91(1) degrees, V = 9392(3) Å(3), 7955 reflections refined to R(w2) = 0.177) were further characterized by single crystal X-ray diffractommetry. Compound 8 is the first example of a monomeric complex of the type LHgX(2) (L = phosphine donor, X = halogen); formation of a halide bridged dimer is presumably prevented by the extraordinarily sterically demanding ligand. A reaction mechanism for the formation of 5 and 8 is proposed which involves the formation of mercury complexes of 1 as the initial step.

Phosphorus Chemical Shift Tensors of Phosphole Derivatives Determined by (31)P NMR Spectroscopy of Powder Samples

The results of a systematic solid-state (31)P NMR study of 5-phenyldibenzophosphole, DBP, its chalcogenides, and some of its transition metal complexes are reported. Phosphorus chemical shift tensors have been obtained from (31)P NMR spectra of stationary samples and of samples spinning about the magic angle. The spans of the phosphorus chemical shift tensors for DBP and its chalcogenides are comparable to those of the corresponding compounds of triphenylphosphine; however, the asymmetry of the tensors for the DBP series reflects the reduced local symmetry at phosphorus. For the complexes (DBP)M(CO)(5) and cis-(DBP)(2)M(CO)(4), where M is a group 6 transition metal (Cr, Mo, W), the most shielded component of the phosphorus shift tensor is found to be relatively independent of the metal or complex, delta(33) = -41 +/- 8 ppm, and is thought to lie along or close to the P-M bond axis direction. In contrast, delta(11) and delta(22) show considerable variation but decrease systematically on descending the group from Cr to W. Group 10 metal complexes, (DBP)(2)MX(2), have also been investigated, including several trans geometric isomers of nickel, cis and trans isomers of palladium, and cis isomers of platinum. The phosphorus shift tensors are nonaxially symmetric with spans in the range 50 -150 ppm. The phosphorus shift tensors of the two nonequivalent DBP ligands of (DBP)(2)PtX(2) (X = Cl, Br) exhibit quite different principal components. The intermediate component of the shift tensor is thought to lie along the Pt-P bond in these complexes. Some of the complexes exhibit interesting MAS-frequency-dependent (31)P NMR spectra.