Phosphido complexes structures

One of the first isolated and structurally characterized phosphido complexes [(t-Bu Ph"N)3Mo=P] (la) was obtained from the reaction of a molybde-num(III) complex with P4 in 79% yield (Eq. 1) [8]. The molybdenum starting material [(f-Bu Ph"N)3Mo] is planar, and the three unpaired electrons are localized on the Mo atom [10], engendering an ideal environment for the reduction of white phosphorus and formation of the triple bond, la can transfer the phosphido ligand to another complex [(t-BuPhN)3Moj via a het-erocumulene intermediate to give [(t-BuPhN)3Mo=Pj (lb) [11] (Eq. 2). 

The phosphido complex, U(PPP)4 [165825-64-9] (PPP = P(CH2CH2P(CH3)2), was prepared and fully characterized (216). This complex was one of the first actinide complexes containing exclusively metal-phosphorus bonds. The x-ray structural analysis indicated a distorted bicapped triganol prism with 3—3-electron donor phosphides and 1—1-electron phosphide, suggesting a formally 24-electron complex. Similar to the amido system, this phosphido compound is also reactive toward insertion reactions, especially with CO (216). 

The homoleptic phosphido complex, Mo(PCy2)4, is produced by reacting LiPCy2 with MoCl4(thf)2 in thf at — 80 °C. A distorted tetrahedral structure, with planar MoPC2 units and an average Mo—P distance of 2.265(2) A, has been established by X-ray diffraction.693... 

Insertion of PhNCS and CS2 into the Zr-P bond of the chlorozirconocene primary phosphido complex 923, which is prepared by the reaction of the zirconocene dichloride with LiPhCy, yields the corresponding insertion products 924 and 925, respectively (Scheme 232).701 The molecular structure of the complex 924 confirms the -bonding mode of the iV-ligation. 

U-Phosphido complex Cp"CpTa(/u-CO)(/u,-PMe2)-W(CO)4 (Cp" = l-Bu -3,4-Me2-C5H2) reacts with an optically active phosphine (PRR R") to give a pair of optically active diastereoisomers Cp"CpTa(CO)(/u,-PMe2)W(CO)4 (PRR R"). X-ray structure determinations of these diastereoisomers lead to the assignment of absolute configurations of the Ta chiral centers. ... 

In the more complex metal phosphines (phosphides) the nature of the M-P bond appears to depend on what other groups are presait in the remainder of the molecule. Preliminary considmtions suggest that the covalent metaUophosphine form of (8.27a) may exist with pj or phosphido-type structures (8.44) while (8.28a) may participate in pj or phosphinidene-type coordination (8.45). 

The phosphido complex anion (Ph2P)4Cd( J,PPh2)6 has a P4O10 (adamantane)-type structure (Table 4.14) which can be compared with the similar (PhS)4Cd(SPh)g. 

As described in Chapter 2, phosphines have sufficiently large barriers to inversion that phosphines with three different substituents can be resolved. In contrast, the inversion of configuration at phosphorus in metal-phosphido complexes tends to occur near room temperature. In imsaturated transition metal complexes, a vacant acceptor orbital stabilizes the planar transition state. This effect is shown by the interconversion between pyramidal structures through a planar transition state, like the one shown in Equation 4.101 and formed during inversion of related compounds. - In saturated middle and late transition metal complexes, inductive effects explained below destabilize the groimd state and lead to lower barriers to inversion. The presence of an ancillary planar phosphide or amide ligand can contribute to a low barrier by accepting the lone pair from a p)Tamidal phosphide, as in Equation 4.101. 

A series of phosphido complexes has been examined. The structure of Cp 2Th(PPh2)2 shows no evidence for significant Th-P multiple bonding.When the lutetium complexes (39) was structurally characterised it was shown to contain a puckered 4-membered ring. The complex (40) has been proposed to contain a platinum-thorium bond. Carbon-hydrogen bond activation including cyclometallation reactions have been reported for Cp 2ThR2 complexes.The first enolate complexes of the type [Cp 2Y(u-OCH=CH2)]2 have been described... 

Phosphido-bridged multinuclear complexes have been formed from zinc chloride of the form [Zn4(PPh2)4Cl4(PRR 2)2], where R and R are alkyl or phenyl groups. Related tetrameric structures can be formed with a bridging dialkyl phosphide or (trimethyl)silylphenyl phosphide.303... 

Cross-coupling to form carbon heteroatom bonds occurs by oxidative addition of an organic halide, generation of an aryl- or vinylpalladium amido, alkoxo, tholato, phosphido, silyl, stannyl, germyl, or boryl complex, and reductive elimination (Scheme 2). The relative rates and thermodynamics of the individual steps and the precise structure of the intermediates depend on the substrate and catalyst. A full discussion of the mechanism for each type of substrate and each catalyst is beyond the scope of this review. However, a series of reviews and primary literature has begun to provide information on the overall catalytic process.18,19,22,23,77,186... 

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