Ligands diphosphene

With increasing electronegativity of one ligand in the diphosphene the ZPPR angle shrunk and decreased finally below 90° for the diphosphene 27. The experimental findings were accompanied by the quantum chemical calculations. There are no other reports regarding further experimental investigations or possible dicoordination in these compounds. 

The investigations indicate that, in agreement with the calculations on the cations, the push-pull substituted diphosphenes tend to form a bridged structure of one ligand the other substituent can easily depart under formation of an ion pair structure. 

The group of Protasiewicz, who has reported Cp2Zr complexed phosphinidenes with very bulky substituents and phosphine ligands, has explored the interchange of ligands and the formation of diphosphenes [113]. 

A novel mode of coordination of diphosphenes is seen in the ligand... 

Complexes with diphosphenes, phosphabenzene, biphosphinine, and other unsaturated phosphorus donor ligands... 

Solventless arylations of norbornene have been reported recently with low ee s (4.5%), in the presence of a chiral diphosphene ligand (Equation (150)).127... 

As with the structure of 160, which contains Te2 as a six-electron donor, comparisons can be made with the coordination chemistry of diphosphenes (RP = PR) (152). Scheme 2 illustrates that 170 can also be formed from 167 and 166, but a similar reaction between 167 and [Mn(CO)2(THF)(CsH5)] affords the cluster complex 171, which contains another example of a Te2 ligand acting as a six-electron donor. Complex 171 is thus very similar to 160. 

Even though great advances in the chemistry of the P=P double bond have taken place over the past two decades, new and interesting diphosphenes, some utilizing sterically demanding m-terphenyl ligands continne to be reported. 

Studies of the reactivity of diphosphenes and phospha-arsenes which bear a complexed transition metal substituent at phosphorus (or arsenic) continue to appear.Aspects of the coordination chemistry of diphosphenes also continue to receive attention.The phosphorus and arsenic analogues of cyclobutadiene, cyclo-P and cyclo-As, have been stabilised as ligands at a niobium centre. 

Like the related diphosphenes, diarsenes are potential donors towards low oxidation state transition metals via either the arsenic lone pairs of electrons or through the n bond itself. In two chromium pentacarbonyl complexes investigated, one of the arsenic atoms donates a lone pair of electrons and the double bond remains essentially intact, increasing marginally from 2.224 A in the uncomplexed ligand to 2.246 A after coordination - . 

P, As, Sb, or Bi), PN, phosphorins, phospha-alkenes and diphosphenes to act as complex ligands has been reviewed. Other reviews have been concerned with PF complexes, metal carbonyls containing ligands of biological significance e.g. porphyrins, nucleosides and amino acids, and carbonyl phosphine clusters of... 

Phospha-alkenes RP=CR 2 can give a complexes (P ligands) and jt complexes (the ligand is the double bond). Interconversion is sometimes observed between these two types of complexes as in [Pt(PPh3P)2(ArP=CPh2)] due to the low energy difference between the a and k phosphorus orbitals, jt complexes of diphosphenes RP=PR are also known in which the P atoms are electrophilic. 

A plausible mechanism for the formation of 32-35 includes prior formation of the corresponding nickel(II) or palladium(II) tetraphosphanediide species, which give the Ni or Pd bis(dimesityldiphosphene) complexes after an intramolecular redox reaction. These intermediates eliminate a diphosphene ligand to give the observed products 32-35 (Fig. 4.14). 

On the other hand, the P H NMR spectrum of 37 consists of a set of three signals corresponding to an AA BB XX spin system (Table 4.1), which indicates that the dianionic P4 chain with the expected dW-trans conformation is retained in solution, as was observed in its molecular structure determined by X-ray diffraction. In the solid state, the nickel atom and the four phosphorus atoms of the chain form a puckered five-membered ring (Table 4.2). Interestingly, the nickel atom has pseudo-octahedral coordination, with the diphosphene ligand (P5 and P6) and the terminal phosphorus atoms of the (P4Ph4) ligand (PI and P4) in the equatorial positions, and the potassium atoms (K1 and K2) in the axial positions with short K--Ni distances of 318.5(2) pm for K1 and 310.7(2) pm for K2, which are the shortest distances reported for an Ni -K interaction in a complex (Fig. 4.18). 

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