Phosphido complexes

Phosphido complexes may be either terminal (8.125a-c) or bridging (8.125e-i). 

Interatomic distances obtained from crystal structure analyses indicate that in some complexes metal-metal bonding is involved as in (8.125i), while in others (8.125d-f) it is not. In the reduced product of (8.125i), namely [Ph2P - W(CO)4] +, there is no W-W bonding. 

Both terminal and bridging phosphido groups can be present in some complexes [51,52]. 

Some terminal complexes can be obtained from alkali metal phosphides (8.127), while bridged complexes can be made by reaction of primary phosphines with halogen bridged complexes (8.128) or by condensation (8.129). 

Thermolysis of Pt(PPh3)4 in benzene gives deep-red solutions from which (8.130) can be obtained. Semiconducting polymers of type (8.131b) can be obtained from such compounds as (8.131a) [53,54]. 

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. 

Additional studies have shown that the P-H bond is much more acidic than its N-H counterpart the piC of PH in DMSO is 24,16 units lower than that of NHj the pX of R PH in DMSO is 34, while that of ArjPH is 22. Coordination increases the acidity of primary and secondary phosphines alkoxides deprotonate the coordinated secondary phosphines but not the free phosphines.  

The enhanced nucleophilicity of a pyramidal phosphide P has been used by Bergman and Toste and by Glueck to develop the catalytic enantioselective synthesis of P-stereo-genic phosphines depicted in Equation 4.102. The system reported by Bergman and Toste involves [(R,R)-MeBPE]2Ru(H)(PMePh) as the phosphido intermediate and Na(OCMejEt) as the base the system reported by Glueck involves Pt[(R,R)-MeDuphos](Ph)(PMeAr) as the phosphido intermediate and Na(OSiMe.) as the base.  

HOMO Of CpRe(NO)PPh3 and the MO diagram resulting from its interaction with a phosphido ligand. 

CHAPTER 4 COVALENT (X-TYPE) LIGANDS BOUND THROUGH METAL-HETEROATOM BONDS 

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The phosphido complex, Th(PPP)4 [143329-04-0], where PPP = P(CH2CH2P(CH2)2)2) has been prepared and fully characterized (35) and represents the first actinide complex containing exclusively metal—phosphoms bonds. The x-ray stmctural analysis indicated 3-3-electron donor phosphides and 1-1-electron phosphide, suggesting that the complex is formally 22-electron. Similar to the amido system, this phosphido compound is also reactive toward insertion reactions, especially with CO, which undergoes a double insertion (35,36). 

O-Bond metathesis of the Ln-alkyl with the phosphine gives a Ln-phosphido complex. (This initiation step was observed to be faster when the hydride derivative [Cp 2bnH]2 was used.) Since the reactions were zero-order in substrate, the next... 

The nitrido and phosphido complexes of TMs have been the subjects of intensive experimental studies in the recent years. Of particular interest has been the issue of Lewis basicity of the nitrogen and phosphorus atoms in the TM=N and TM=P groups. Table 7.17 lists the BDEs calculated at the MP2/II, B3LYP/B and CCSD(T)/B levels of theory for LnMN-X and LnMP-X, where X is a group-13 Lewis acid or a chalcogen atom [86, 87]. 

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). 

Table 1 M=P bond lengths and P-NMR data of terminal phosphido complexes of type A...

To prevent the latter mentioned subsequent reactions, the bulky phos-phaalkyne Ph C P as well as tungsten alkoxides of reduced size as, e.g., [W2(ONp)6] were employed in these three-component reactions with no significant success [15]. The crucial steps for the side-product free synthesis of the phosphido complexes 18 are the introduction of a phosphaalkyne possessing a moderate steric bulkiness, which lies between those of f-BuC=P and Ph C P, and resulting from the P-NMR studies (cf. Eq. 5), a reaction temperature mode allowing the complete metathesis reaction to take place at very low temperatures over a long period of time until all the phosphaalkyne has been converted into the metathesis products (about 12 h) only then is the reaction mixture allowed to reach room temperature. We found that MesC=P meets these steric requirements, and the three-component-reaction between MesC=P, [W2(Of-Bu)6] and [M(CO)5(thf)] (M = Cr, W), carried out at -78 °C and warmed up to ambient temperature within 15 h, succeeded in the synthesis and isolation of the phosphido complex 18a,b (Scheme 2) [15]. Furthermore, if t-BuC=P is incorporated into these reactions, the steric requirements of the alkoxide dimer has to be slightly increased. Thus, f-BuC=P reacts with [W2(OPh )6] and [M(CO)5(thf)] (M=Cr, W) under the... 

From a comparison of the data in Table 1 and Table 2, coordination of the phosphido complexes 3c and 4a,b to a Lewis acidic fragment generally leads... 

Fig. 3) show n orbitals to be the HOMO orbitals. Thus, the primary reactivity pattern should be the side-on reactivity. However, this reactivity is generally not allowed in the phosphido complexes with tris-amido ligand sets due to their kinetic stabilization by bulky substituents. Therefore, experimentally, only the less crowded and more flexible alkoxide complexes 18 and 21 show the anticipated side-on access to the triple bond. 

Furthermore, the phosphido complex 21b reacts with [(PPh3)2Pt (/7 -C2H4)] to give the dinuclear complex [(Ph 0)2WPt(PPh3)( -PPh2) ( -PPh)W(CO)5 j (25) which also possesses a planar WP2Pt four-mem-... 

Acyl(phosphido) complexes, with Pt(II), 8, 458 Acyl radicals, via selenium precursors, 9, 477 Acylsilanes, applications, 9, 319 Acylstannanes, preparation, 3, 822-823 l-Adamantyl-2-pyridyl amido complexes, with Zr(IV), 4, 782 Adaptive quantum control, for selective bond cleavage, 1, 247 Addition reactions... 

The thermolysis of Pt(PPh3)3 and related compounds gives di- and trinuclear phosphido complexes, evidently via oxidative P—C bond cleavage. 

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