Phosphine complexes tertiary

Tertiary phosphine complexes [42] are the most important rhodium(I) compounds. RhCl(PPh3)3 ( Wilkinson s compound ), a hydrogenation catalyst, is the most important, but they exist in a range of stoichiometries. Synthesis follows several routes  

Displacement of CO, only possible with strong 7r-acids 

Reduction using certain arylphosphines as reducing agents 

The ability of triphenylphosphine to act as a reducing agent probably involves initial formation of Ph3PCl2, which then undergoes solvolysis. If the synthesis is carried out using a small volume of ethanol, an orange polymorph is formed [45]. 

There are, however, short Rh-H contacts (2.77-2.84A) to ortho-hydrogens in phenyl groups. The Rh-P bond trans to Cl is some 0.1 A shorter than the others, evidence of the weak franj-influence of chloride [46]. 

Tertiary phosphine complexes have been studied intensively since the 1960s. The bulk of the work has been with phosphines, but corresponding arsine complexes are broadly similar. 

In general, the dimers have three chlorine bridges, and Ru3C18(PBu3)4 resembles the mixed-valence chloro complex Ru3Clt2. A similar, but less extensively studied, pattern of behaviour has been found with other alkyl phosphines. 

The axial resonance is assigned to ruthenium A with its D4h local symmetry (compare g = 2.51, g = 1.64 in lra 5-RuCl4(PEt3)2) while the rhombic signal is assigned to ruthenium B , where the local symmetry is D2h and three different components of the g-tensor are expected. 

The bidentate phosphine complexes were among the earliest ruthenium phosphine complexes to be made [85] often displacement is a convenient route  

All the compounds of the type RuH2(PR3)4 seem to be classical hydrides 

RuCl2L2(PPh3)2 Ru(acac)2lPPh,)2 (both isomers. L = CO, MeCN) 

The osmium(VI) complexes 0s02X2(PR3)2 are not generally obtainable with the smaller alkyl and alkyl(aryl)phosphines, which tend to be good 

These compounds give characteristic osmyl IR bands (840 cm 1 in 0s02Cl2(PPh3)2) [151]. 

The osmium(IV) complexes are only obtained by this route with fairly unreactive phosphines and arsines (e.g. PBu2Ph) but they are conveniently made by oxidation of mer-OsX3(QR3)3 (Q = P, As) with the halogen in CHC13, or CCI4 and refluxing. 

Distinguishing between the fac- and mer-isomers is theoretically possible with far-IR spectra, as the mer-isomer (C2v symmetry in the coordination sphere) should give rise to three u(Os—X) stretching bands, while the C3v 

OsCl2(PPh3)3 PMe3 trans-OsCl2(PMe3)4 

The magnetic moments for these osmium(III) complexes are, as expected, in the range 1.9-2.2 Reduction of wer-OsX3(PR3)3 has been studied in 

The action of light has been used to effect the isomerization of tertiary phosphine complexes. When the planar d complexes cw-PtX2(PPh3)2 (X = Cl, Br) are irradiated at 366 nm, isomerization to /ran -PtX2(PPh3)2 is observed. The reaction is both reversible 

More interest, however, has been focused on the photochemistry of phosphine complexes of the second- and third-row transition metals in their lower oxidation states. This interest is primarily the result of the fact that such complexes are widely used as homogeneous catalysts in the solution phase, and it is theorized that photochemical techniques can be used to generate reactive excited states, or at least to generate reactive, coordinately unsaturated species. A primary goal of such work is the generation of a photocatalytic system whereby the photoproduct is a thermal catalyst, thereby making the transformation catalytic in the number of incident photons. Many of these ideas that have been pursued with tertiary phosphine complexes have also been followed for transition metal carbonyl complexes, with this latter photochemistry being discussed in Chapter 6. 

The d phosphine and phosphite complexes of zerovalent nickel, palladium and platinum possess long-lived emissive excited states in both fluid solution and in the solid state.The lifetimes of the Ni and Pd complexes are in the 1.39-5.38 ps range, with the platinum complex Pt(PPh3)4 having the shorter excited state lifetime of 0.07 //s because of spin-orbit coupling. These long lifetimes allow for bimolecular reactions to occur, and under photochemical conditions chlorobenzene will add to the complex Pd(PPh3)3 (Ref. 75)  

Pd(PPh3)3 + C6H5CI ran5-PdCl(C6H5)(PPh3)2 + PPh3 (3.18) 

When the chelating diphosphine bis(diphenylphosphino)propane (dppp) is used in place of triphenylphosphine, the emission lifetimes of the complexes M(dppp)2 (M = Pd, Pt) are shorter ( 0.02 ps). For these chelate complexes, ligand dissociation is less favorable, and irradiation ( 340 nm) of Pd(dppp)2 in CH2CI2 now gives [Pd(dppp)2]Cl2 and ethylene rather than the alkyl halide addition product  

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With certain transition metals, eg, Ru(II)-tertiary phosphine complexes, the principal products are bis(epoxides) (82). 

Figure 1.22 Syntheses of tertiary phosphine complexes of ruthenium.

Within the osmium complexes in oxidation states (II-IV) [11,12] the stability of the +4 oxidation state becomes more important. Ammine and tertiary phosphine complexes have been selected for detailed examination. 

Syntheses of some of these important tertiary phosphine complexes are summarized in Figure 1.60, which represent reactions typical of a tertiary phosphine (e.g. PMe2Ph), showing complexes in the oxidation states +6, +4, +3 and +2 [78a]. 

NMR spectra of tertiary phosphine complexes are often helpful in assigning stereochemistries [114] and two examples of mer-isomers are illustrated here. 

The tertiary phosphine complexes are the most important zerovalent compounds. They are frequently prepared by reductive methods, often using the phosphine as the reducing agent [43], e.g. 

In addition to the tertiary phosphine complexes, a few others such as Pt(QBu3)4 (Q = As, Sb) and Pt(QPh3)4 have been made, but they have been the subjects of few studies. 

Tertiary phosphine complexes of platinum and palladium M(PR3)2X2 are important [95]. The cis- and trans- somers are readily obtained for platinum,... 

A number of tertiary phosphine complexes with bulky ligands (Figure 3.80) have modified square pyramidal structures, examples being M(I)3Br2, Pt(II)3Br2 and Pd(III)3Br2 (all X-ray) [136]. 

The most important of the tertiary phosphine complexes of platinum(IV) are Pt(QR3)2X4, generally prepared by halogen oxidation [174] of cis- or trans-Pt(QR3)2X2 (Q = P, As, R = alkyl Q = Sb, R = Me), since direct reaction of the platinum(IV) halides with the ligands leads to reduction. Once made, the platinum(IV) compounds are stable to reduction ... 

A variety of methods have been reported for synthesizing platinum(O) tertiary phosphine complexes and a range of standard methods have been described in a series of reports in... 

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