Containing metal-phosphorus bonds

Trivalent and pentavalent phosphorus halides will form addition complexes with metals or metal salts. While the trivalent complexes contain metal-phosphorus bonds (Chapter 8), the pentavalent complexes involve rearrangements to produce ionised assemblies of tetrahedral PX4 cations and various complex anions. 

In many of their complexes PF3 and PPI13 (for example) resemble CO (p. 926) and this at one time encouraged the belief that their bonding capabilities were influenced not only by the factors (p. 198) which affect the stability of the a P M interaction which uses the lone-pair of elecU"ons on p and a vacant orbital on M, but also by the possibility of synergic n back-donation from a nonbonding d , pair of electrons on the metal into a vacant 3d , orbital on P. It is, however, not clear to what extent, if any, the a and n bonds reinforce each other, and more recent descriptions are based on an MO approach which uses all (cr and n) orbitals of appropriate symmeU"y on both the phosphine and the metal-containing moiety. To the extent that a and n bonding effects on the stability of metal-phosphorus bonds can be isolated from each otlier and from steric factors (see below) the accepted sequence of effects is as follows ... 

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 tetrakis(dialkylphosphido) complexes, An(PPP)4 (An = Th, U) PPP = P(CH2CH2P(CH3)2), were prepared by reacting AnC with four equivalents of the lithium or potassium salt of the PPP tetra-anion. The stmcture of these compounds shows triangulated dodecahedra distorted toward bicapped trigonal prisms. These complexes represent one of the first actinide systems containing exclusively metal-phosphorus bonds. These complexes are known to undergo insertion reactions as seen in actinide amido compounds. ... 

Phosphites, like phosphines, form coordination complexes which are characterised by direct metal-phosphorus bonding using lone-pair electrons on the P atom. Their relationship to other O-containing complexes is indicated in Table 8.16. 

A few final comments should be made on the insertions of substrates containing C-C multiple bonds into the bonds between a transition metal and an electronegative heteroatom. First, insertions of olefins into related thiolate and phosphide complexes are as rare as insertions into alkoxo and amido complexes. Reactions of acrylonitrile into the metal-phosphorus bonds of palladium- and platinum-phosphido complexes to give products from formal insertions have been observed, and one example is showm in Equation 9.90. However, these reactions are more likely to occur by direct attack of the phosphorus on the electrophilic carbon of acrylonitrile than by migratory insertion. Second, the insertions of alkynes into metal-oxygen or metal-nitrogen covalent bonds are rare, even though the C-C ir-bond in an alkyne is weaker than the ir-bond in an alkene. 

In this book we are concerned with the properties of compounds which contain metal—carbon bonds. Traditionally organometallic chemistry includes the carbon compounds of the metalloids boron, silicon and arsenic, but excludes those of phosphorus and of other more electronegative elements. Metal carbonyls are discussed, but not cyanides or carbides, which are more usefully considered in conjunction with inorganic rather than organometallic compounds. 

The metallation of thiophen and 2- and 3-methylthiophen with butylcaesium and butylpotassium has been studied. Thienylcopper reagents have been used for the synthesis of iodo-thiophens. Thienyltin(iv) compounds have been prepared. The chemistry of thienyl-lead(iv)tricarboxylate has been investigated. The cleavage of the thiophen-silicon bond in tris(trichloro-2-thienyl)-methylsilane with butyl-lithium to give thienyl-lithium derivatives has been achieved. Considerable work on the synthesis and reactions of compounds containing thiophen-phosphorus bonds has appeared/ " and the reactions with a/S-unsaturated acid derivatives have been extensively studied. ... 

Phosphorus acids containing P—S bonds in which the sulfur atom acts as the metal ligating atom also received much attention.243,252,255-261 The commercially available reagents bis(2,4,4-trimethylpentyl)phosphinothioic acid (Cyanex 302) and bis(2,4,4-trimethylpentyl)dithiophosphinic... 

The breaking of carbon-to-phosphorus bonds is by itself not a useful reaction in homogeneous catalysis. It is an undesirable side-reaction that occurs in systems containing transition metals and phosphine ligands and that leads to deactivation of the catalysts. Two reaction pathways can be distinguished, oxidative addition and nucleophilic attack at the co-ordinated phosphorus atom (Figure 2.35). 

In 1995 a breakthrough occurred in this field in February we were able to show the synthesis and the spectroscopic properties of the first complexes of type B [7], and in August the first isolated and structurally characterized complexes containing terminal metal-phosphorus triple bonds (type A) were independently obtained and published in back-to-back articles by the groups of Cummins [8] and Schrock [9]. Since then, a rapid development has occurred in the synthesis and particularly in the study of the reactivity pattern of complexes with phosphorus-transition metal triple bonds. This review chapter will highlight the development in this field by giving an overview from 1995 until the current stage of research. 

By writing about complexes containing triple bonds between phosphorus and transition metals, one has to take into account the triple-bond character of phosphinidene complexes which are in a nearly linear coordination mode (type C) in contrast to the usual bent coordination mode D possessing typical double-bond features. Due to the additional r-donation bonding ability of the PR moiety to the metal atom in type C and the observed bond lengths, this type of complexes has to be included into the classes of metal-phosphorus triple bond compounds. Thus, at the end of this review will appear a chapter highlighting the appropriate compounds of type C. 

In the first structurally characterized complexes of type A the metal-phosphorus triple bonds are kinetically stabilized by bulky substituents at the amido ligands. Therefore, these compounds reveal exclusively end-on reactivity via the phosphorus lone pair. This reactivity pattern seems also valid for the solution stable alkoxide derivative [(C/0)3Mo=P], for which the reaction potential is under investigation [13]. In contrast, due to their lesser degree of kinetic stabilization by bulky substituents the short-lived alkoxide containing complexes [(R 0)3W=Pj (R =t-Bu (3c), Ph (3d)), generated by the metathesis reaction between the alkoxide-dimer and the phosphaalkyne (cf. Eq. 8), show additionally a high side-on reactivity towards the phos-phaalkynes of the reaction mixture. Thus, there occurs a formal cycloaddition reaction with the phosphaalkynes, and a subsequent 1,3-OR shift yields the formation of four-membered diphospha-metallo-cyclobutane derivatives 6(Eq. 8) [15,31, 37]. 

Our experience has shown that the hydrolysis of aluminium phosphide with cold water is the most suitable method for the laboratory preparation of phosphine. Here it is important that the aluminium phosphide be as pure as possible in order to avoid the formation of spontaneously inflammable phosphine. The presence of small quantities of diphosphine and also higher phosphines are responsible for this spontaneous inflammability 96.276-278) jj. gp, pears, however, that these are only formed when P—P bonds are already present in the phosphide. Accordingly the hydrolysis of aluminium phosphide, prepared from the elements with phosphorus in slight excess, always leads to spontaneously inflammable phosphine. The formation of diphosphine and higher phosphines from aluminium or alkaline earth metal phosphides, which contain excess phosphorus, can be easily understood when the lattices of these compounds are considered. 

In all the above reactions the hydrido phosphorus centre acts as a pen-tavalent phosphorus. Interesting reactions are known in which the tautomer of the hydridophosphazene containing a P(III) centre acts as a trivalent phosphine towards transition metals. Thus N3P3Ph4(Me)H on treatment with MCI2 (M = Pd, Pt) [246] or AUCI3 [247] results in complexes [N3P3Ph4(Me)H]2 MC1 (M = Pd or Pt n = 2, M = Au n = 3). These complexes have been shown to possess phosphorus-metal coordinate bonds (Eq. 49). 

We may classify solids broadly into three types based on their electrical conductivity. Metals conduct electricity very well. In contrast, insulators do not. Insulators may consist of discrete small molecules, such as phosphorus triiodide, in which the energy necessary to ionize an electron from one molecule and transfer it to a second is too great to be effected under ordinary potentials.M We have seen that most ionic sefids are nonconductors. Finally, solids that contain infinite covalent bonding such as diamond and quartz are usually good insulators (but see Problem 7.5). 

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