M-P bonds

These composite BDE values increase strongly on substituting the phosphorus atom with n-electron donating groups. However, this substitution effect does not relate to strengthening of the M=P bond,but rather reflects a reduction in the AEji of tho froo phosphinidene or conversely an increase in the AEji for the complexed phosphinidene. Still, as a point of reference, it is noted that similar CASPT2 and BP values of 41.1 and 40.5 kcal/mol, respectively, have been deduced for the dissociation of the parent Cr complex (OC)5Cr=PH into CrfCO) and PH. 

Multiple M=P bonding in (OC)5M=PR becomes evident with ADF s bond energy analysis in terms of electrostatic interactions, Pauli repulsion, and orbital interactions from which the a,Ti-separation is obtained using a symmetry decomposition scheme [21]. For singlet (OC)5Cr=PR, which has a BDEst of 40.5 kcal/mol, the a- and n-components are 62.4 and 40.9 kcal/mol, respectively. 

Electrophilic and nucleophilic phosphinidene complexes have been related to the corresponding carbene complexes of which the Fischer-type is usually considered as a singlet-singlet combination and the Schrock-type as a triplet-triplet combination. However, both the strongly preferred triplet state of R-P and the M=P bond analysis suggest this schematic interpretation to be less appropriate for transition metal complexed phosphinidenes. 

Table 4. M=P bond distances, M=P-R bond angles, and P NMR chemical shifts of stable cationic terminal phosphinidene complexes ...

The 31P and H study revealed the configuration of the central atom and the conformation of the cyclic ligand fragments, as well as the orientation of M—P bonds. The Pt—P bond is equatorial in the 1,3,5-diazaphosphorinane cycle. 

With a metal ion having four coordination centers, binding of four molecules (39) can occur. The reaction of four molecules of (39) with Hg(II) perchlorate in CH3CN produced complex (212) with a high yield [Eq. (150)]. Electrochemical oxidation of some phosphines on a mercury anode has been shown to lead to their complexes with Hg(II). Following this method, complex 212 was synthesized in high yield (92MI1). The M—P bonds were shown to be in an equatorial position. 

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

Stretching frequencies and force constants for the M=P bond have been derived from Raman spectroscopic data for compounds [(N3N)Mo=P] (4a) and [(N3N)W=P] (4b), as well as for related nitrido and arsenido complexes [30]. For W=E (E = N, P, As), force constants were shown to decrease with increasing M=E bond length, while for each respective pnicogenido ligand E, the force constant for the W complex was greater than that of the Mo complex, a trend also reflected in literature data for transition metal nitrido and 0X0 complexes [20]. 

Table 3 P-NMR data, M-P bond lengths, and M-P-Q bond angles of representative phosphinidene complexes ...

Attempting to rationalize the strength of a metal-phosphorus bond in terms of the collective a, tt, and steric capacity of a coordinated phosphine is a difficult matter. Refer to the series you developed in Problem 11.13 and predict which ligands would form the strongest and the weakest M—P bonds. 

In cluster formation the ligand may be viewed from the cluster as a whole rather than the particular metal atom forming the M—P bond, i.e. the cluster-phosphine distance that determines... 

The substantially larger values of M-p for phosphorus trans to chlorine compared with phosphorus trans to phosphorus correlate with shorter M-P bonds trans to chlorine for a number of metals and oxidation states tungsten(IV), rhodium(I) and (III), platinum(II) and (IV), and linear mercury(II) (15). By analogy with the discussion of the results for the platinum(II) complexes, this indicates the dominance of the (P sMSp)2 term in Equation 1 for couplings with a variety of M, but as discussed earlier it is difficult to determine the extent of variation of... 

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