Phosphines bonding

Schwerdtfeger, P., Hermann, H.L. and Schmidbaur, H. (2003) The Stability of the Gold - Phosphine Bond. A Comparison with other Group 11 Elements. Inorganic Chemistry, 42, 1334—1342. 

An X-ray crystal structure of [Rh(PF-PPh2)(COD)]PF6 reveals a distorted square-planar geometry around rhodium (Fig. 4.1). The Rh-phosphaferrocene bond length (2.25 A) is shorter than the Rh-(tertiary phosphine) bond length (2.30 A). We postulated that the strong -accepting capacity of the phosphaferrocene [9] may lead to effective Rh P back-bonding that decreases the conformational flexibihty of the metal-... 

The nature of the Niu—P bond in pseudotetrahedral phosphine complexes has received much attention. With the AOM Gerloch et al. showed that phosphine bonds are characterized by a large o basicity and large it acidity corresponding to a back-donation of electrons from the nickel to the phosphorus atom in both mono and bis phosphine complexes.549,550... 

Metal-phosphine bonds can generally be modeled in much the same way as any other metal-heteroatom bond. The fact that phosphines participate in x-backbonding (filled dn (metal) -> empty d or a (phosphorus) interaction) is only of importance for generic force field parameterization schemes, and half-integer bond orders have been used to describe the effect of x-back-donation[ 153). In the usually adopted empirical force field formalism, x-bonding effects, like most of the other structural/elec-tronic effects, are accommodated by the general parameter-fitting procedure (see Parts I and III). 

Aluminum nitrides, for semiconductor growth, 12, 2-3 Aluminum(III)-nitrogen bonds covalent and non-covalent, 9, 255 mixed covalent and non-covalent systems, 9, 258 Aluminum nucleophiles, in conjugate additions, 10, 389 Aluminum(III)-oxygen bonds covalent and non-covalent, 9, 252 mixed covalent and non-covalent systems, 9, 258 Aluminum(III)-phosphine bonds, covalent and non-covalent, 9, 259... 

It is also found (Table 11) that Jpoi is smaller for phosphole complexes than for similar phosphine complexes demonstrating that there is less s-character in the platinum phosphole bond than in the platinum phosphine bond. Since the platinum s-orbital character is probably constant, this signifies less phosphorus s-character in the phosphole... 

Insertions into transition metal-phosphine bonds have been observed, as shown in reactions (s) °, (t) and (u). ... 

Historically, the theoretical background to bonding of Group 15 ligands to metals has been developed for phosphines, and treatment of the heavier analogs is in terms of the trends down the group and any differences relative to the PR3. In recent years the metal-phosphine bonding model... 

Figure 8.8. Illustration of two types of metal-phosphine bonding that can occur with supported monophosphine ligands.

Recently in the Sijbesma group, high-molecular-weight linear coordination polymers of diphenylphosphine telechelic polytetrahydrofuran with palladium (II) dichloride were developed [3]. Molecular weights of these polymers could be altered reversibly by ultrasotmd and it has been shown that polytetrahydrofuran chains remain intact during sonication [78]. This implies that only the reversible palladium-phosphorus bonds are broken and coordinatively unsaturated palladium complexes were produced by the application of mechanical forces on these coordination polymers [79]. Furthermore, polymers which include both Pd and Pt were sonicated and it was shown that force selectively breaks the weaker Pd-phosphine bonds which were randomly distributed along the polymer backbone [80]. 

Figure 7.22 Phosphine bond dissociation energies at OK (i.e., including zero-point vibrational energies) for the first- and second-generation ruthenium-based Grubbs catalysts, as calculated and obtained in ESI-MS experiments. (Adapted from Ref. [85]).

The dendrimers were more efficient catalysts than the monomeric model complex. This could possibly be due to labilization of metal-phosphine bonds that is facilitated in dendrimers as eompared to the monomer for entropic reasons. Indeed, DFT ealeulation showed that the catalytic process must involve decoordination of a phosphorus atom, since the interaction of the olefin with the diphosphine complex is nonbonding." The dendritic Ru-benzylidene dendrimers were air-sensitive contrary to the monomer model complex, consistent with more rapid dissociation of the alkyl phosphine in the dendrimers than in the monomer. 

---