Phosphole ligands

The phosphine-phosphole ligand with [Rh(cod)Cl]2 affords complex 254 (99OM4205). 

Table 3 Hydroformylation of styrene in the presence of [Rh(nbd)Cl]2 +4L phosphole ligands at 100°C, 40 bar...

Both four- and five-coordinate platinum(II) complexes can be prepared with phosphole ligands L (119).1328 The complexes /rans-PtX2L2 (X = Cl, Br, I R = Me, Bun, Bu, Ph, CH2Ph R = H, Me) are non-electrolytes in methanol solution. The formation of the five-coordinate adduct (equation 411) can be analyzed in terms of intra- and inter-molecular equilibria of the pentacoordinate species PtX2L3. The formation of PtX2L3 is enthalpy favored and entropy disfavored. 

Coordination Chemistry of Phosphole Ligands Substituted with Pyridyl Moieties From Catalysis to Nonlinear Optics and Supramolecular Assemblies... 

The coordination chemistry of 2-(2-pyridyl)phosphole ligands toward Pd(II) centers was investigated with the aim of gaining insights into their coordination behavior. Thus, the reaction of 3b-d with [(cod)PdMeCl] (cod = l,5-cyclo-l,5-octadiene) afforded the corresponding air-stable complexes 6b-d as single diastereoisomers in excellent yields (Scheme 12.3) [15]. 

In comparison to the other 2-(2-pyridyl)-phosphole P,N-ligands 3c-f, 2,5-bis(2-pyridyl)-phosphole ligand 3b revealed a very original coordination chemistry toward Pd(I), Pt(I), and Cu(I) metal centers. A family of coordination complexes exhibiting a bridging phosphane coordination mode was thus evidenced, a very rare coordination mode for such a commonly used family of ligands. 

X-ray diffraction study revealed that compound 15 is a [Cu2(3b) (CH 3CN)4]2+ 2PFS complex (Figure 12.6) in which two Cu(I) atoms are capped by a 2,5-bis(2-pyridyl)phosphole ligand 3b acting again as a 6-electron p-lkN l,2kP 2kN donor. 

Reaction of chlorobis(methylene)phosphorane 55 with K[(i73-C3H5)Fe(CO)3] in a mixture of THF and toluene gives the metallobis(meth-ylene)phosphorane 56 and the bis(methylene)propenylphosphorane 57 as major products. The dihydrophosphole complex 58 is obtained as a minor product (<10% yield) (Scheme 13).40 In contrast, treatment of 55 with K[Fe(CO)2Cp] gives rise to the formation of the metallobis(methylene) phosphorane 59 (39% yield) and the phosphaferrocene 60 (34-72% yield, dependent upon the reaction time). The phosphole ligand of 60 is con-... 

Complex 196 was obtained by a Diels-Alder reaction involving one coordinated phosphole ligand of 195 and dimethyl acetylenedicarboxylate (Scheme 60) <2002CEJ58>. Thermal decomposition of 196 at 80°C yielded phospholene complex 197 as the major product. 

Another facet of this versatile methodology is its potential for the synthesis of functionalized phospholes, which can be used for further chemical transformations. For example, anion 231, which was prepared by reduction with lithium of the corresponding P-chloro-phosphole and characterized by NMR spectroscopy, is an efficient intermediate for the preparation of functionalized phospholes 232 (66-80% yield) (Scheme 76) <1999OM4205>. These phospholes are useful precursors for the synthesis of mixed phosphinine- and phosphaferrocene-phosphole ligands. The l-(2-cyanoethyl)phosphole was characterized by an X-ray diffraction study <1999OM4205>. 

An important property of metal-bound phosphole ligands is their ability to undergo additional reactions not possible in the noncomplexed form. This is nicely illustrated by the thermally induced reactions of the palladium(ll) complex of 1-phenyl-3,4-dimethylphosphole 341 <1996IC1486>. Heating complex 341 at 145 °C in solution or at 140 °C in the solid state led to the formation of a mixed 7-phosphanorbornene-phosphole complex 343 (Scheme 114). These intramolecular [4-1-2] cycloaddition reactions are believed to proceed via the initial formation of a diallyl 1,4-biradical TS 342. Further examples of this type of reaction may be found in Section 3.15.12.1.1. 

Xanthene-phosphole ligands in the palladium-catalyzed amine allylation <20070M1846>. 

As can be seen by comparing the Pd-P bond lengths in these compounds, the phosphole ligand is quite polarizable and the Pd-P bond lengths are very sensitive to the nature of the trans ligand. The residual aromaticity of the inequivalent phospholes in (DMPP)2Pd(SCN)(NCS) is also quite different, further illustrating the phosphole polarizability. 

The steroidal 1,4-diphosphanes 3x- and 3/ -(diphenylphosphino)-2a-[2-diphenylphosphi-no)ethyl]-5a-cholestane and their 5//-benzo[h]phosphindole derivatives are also used as chiral ligands in hydrocyanation. While the diphenylphosphane ligands lead to moderate optical yields in the hydrocyanation of norbornene in the presence of Pd(BDA)2 (21% yield, 98% product selectivity, up to 39 % ee), the phosphole ligands only give trace amounts of product with no asymmetric induction detectable38. 

Interest in heterophospholes has continued. Routes to the 1,2-thiaphosphole (361), and the l-thia-2,4-diphosphole (362) have been reported. New routes to polyazaphospholes have also been explored, and their reactivity studied. The coordination chemistry of polyphospholide anions has also continued to receive attentionInterest has been maintained in the coordination chemistry of simple phospholes and related phospholide anions. Complexes of l-substituted-3,4-dimethylphospholes with platinum(Il) acceptors undergo thermal dimerisation of the phosphole ligands either in solution at 145°C or in the solid state at 140°C, and three product-types have been characterised by X-ray crystallographic techniques. ... 

Only one report has appeared on five-co-ordination in palladium(ii) and platinum(ii) complexes. In a preliminary note three compounds of the type [M(phos)3Bra], where M = Pd or Pt and phos is a 5-alkyl-5fl-dibenzophosphole ligand (28), are said to involve square-pyramidal coordination about the metal atoms, with all the co-ordinated phosphorus atoms in basal sites. In each molecule two of the planar phosphole ligands are mutually parallel, as was found in the analogous nickel(ii) complexes. No further details are given. 

P-chiral phosphines were obtained from the reactions of ligated phosphole ligands with dienophiles. phosphole ligands were bonded to N,G-palladacycles. Similar reactions of dienes were carried out with diphenyl-vinylphosphine and 2-diphenylphosphinofuran bonded to N,G-palladacycles. ... 

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