Phosphanes, primary complexation

A recent development that has gained attention is the characterization of a remarkable series of complexes resulting from the multiple metallation of primary phosphanes, and also a smaller number of the heavier group 15... 

Reviews covering the chemistry of group 2 metal complexes with phosphorus-stabilized carbanions,279 and of molecular clusters of magnesium dimetallated primary phosphanes, are available.2 u Magnesium phosphanes remain rare compounds.281 Lithiation of bromide 98 with BuLi in the presence of tmeda in pentane produces a lithium phosphine dimer subsequent treatment with MgCl2 in EtzO gives the phosphane 99 in 69% overall yield (Equation (19)). The centrosymmetric 99 has Mg-C = 2.217 A Mg-P = 2.77 A (av.).282... 

The cyclic cobalt-acyl complex 1 undergoes a-proton abstraction from the least-hindered face opposite the phosphane ligand upon treatment with lithium hexamethyldisilazide at 0 °C to generate the chiral enolate species 283. Treatment of 2 with primary iodoalkanes diastereoselec-tively produces the alkylated cobaltocycles 3 also via attack of the reagent on the face opposite the bulky phosphane. 

Naturally, it is possible to synthesise a similar ligand system without central chirality and in fact without the unnecessary methylene linker unit. A suitable synthesis starts with planar chiral ferrocenyl aldehyde acetal (see Figure 5.30). Hydrolysis and oxidation of the acetal yields the corresponding carboxylic acid that is transformed into the azide and subsequently turned into the respective primary amine functionalised planar chiral ferrocene. A rather complex reaction sequence involving 5-triazine, bromoacetal-dehyde diethylacetal and boron trifluoride etherate eventually yields the desired doubly ferrocenyl substituted imidazolium salt that can be deprotonated with the usual potassium tert-butylate to the free carbene. The ligand was used to form a variety of palladium(II) carbene complexes with pyridine or a phosphane as coligand. 

Different procedures were developed for the obtention of Zr phosphinidene complexes. The first stable complex was obtained via the loss of phosphane from an intermediate bis phosphanido complex. Other routes were sought to more readily gain access to these unsaturated complexes. Thus, the addition of a base to a primary phosphanido complex is another opportunity to obtain such complexes. Benzonitrile and dicyclohexylcarbodiimide react with the phosphinidene complex (22) by insertion into the Zr=P bond, or by cycloaddition and subsequent rearrangement (Scheme 5). 

In going from secondary to primary phosphanides, the expected upheld shift in the phosphorus resonance is observed as primary phosphanes are usually found upheld from the respective secondary phosphanes. Substituting a phenyl group with a hydrogen atom does not only create an upheld shift in the phosphorus resonance, but also introduces asymmetry into the complex (see Fig. 7.11). There are now three stereoisomers observable. They are differentiated by the relative positions of the phenyl and hydrogen substituents on the phosphorus atoms. Each of the three isomers has its characteristic multiplet pattern, with accompanying and Jpp coupling constants. 

Xie J, Huang J-S, Zhu N, Zhou Z-Y, Che C-M (2005) Primary and secondary phosphane complexes of metalloporphyrins isolation, spectroscopy, and X-ray crystal structures of ruthenium and osmium porphyrins binding phenyl- or diphenylphosphane. Chem Eur J 11 2405-2416... 

Dell Anna MM, Mastrorilli P, Nobile CF, Calmuschi-Cula B, Englert U, Peruzzini M (2(X)8) Reactivity of mononuclear Pd(II) and Pt(II) complexes containing the primary phosphane (ferrocenylmethyl)phosphane towards metal chlorides and PPh3. Dalton Trans 6005-6013... 

Another synthetic procedure (method 3) for the preparation of metal complexes with linear anionic units is the reaction of primary phosphanes and anionic primary phosphanes with metal complexes [32-34]. For example, the reaction of LiPHPh with [Zr( j"-C5H5)2Cl2] gave [Zr(j/"-C5H5)2(P3Ph3)] (10) (Fig. 4.3) [32]. 

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