Phosphorus coordination

Metal-Phosphorus Bono Lengths, Torsion Angles between the Metal and Phosphorus Coordination Planes, Sums of Angles at Phosphorus, and 3IP NMR Chemical Shifts for Three-Coordinate Aluminum, Gallium, and Indium Phosphides... 

Functionally substituted phosphines play an important role as ligands in a great variety of phosphorus coordination compounds. They have some interesting features that distinguish them from other phosphine ligands, namely (a) the presence of other heteroatoms bearing lone electron pairs in addition to phosphorus (b) the presence of functional groups able to form bonds with a metal with the participation of its valence electrons ... 

Technetium(V) complexes with exclusively phosphorus donors and the [Tc=0] core are obviously not stable. The lack of charge compensation leads to Tc " compounds by further reduction, or to hydrolysis. Pure phosphorus coordination is then possible only if the [0=Tc=0]" core is present, as described in the following section (Scheme 36). 

The iron(II)-iron(III) form of purple acid phosphatase (from porcine uteri) was kinetically studied by Aquino et al. (28). From the hydrolysis of a-naphthyl phosphate (with the maximum rate at pH 4.9) and phosphate binding studies, a mechanism was proposed as shown in Scheme 6. At lower pH (ca. 3), iron(III)-bound water is displaced for bridging phosphate dianion, but little or no hydrolysis occurs. At higher pH, the iron(III)-bound OH substitutes into the phosphorus coordination sphere with displacement of naphthoxide anion (i.e., phosphate hydrolysis). The competing affinity of a phosphomonoester anion and hydroxide to iron(III) in purple acid phosphatase reminds us of a similar competing anion affinity to zinc(II) ion in carbonic anhydrase (12a, 12b). 

Even chlorine which is bound to phosphorus coordinated to a metal atom can be exchanged for fluorine, but higher temperatures are required. So the four-membered phosphido-bridged metal complex 16 is fluorinated at temperatures over 100C, whereas the exchange reaction in the case of the corresponding iodide proceeds at room temperature and for the bromide at over 60CC in 80% yield each.77... 

Our third contribution is by Alexander Sadimenko, of the University of Fort Hare, (Republic of South Africa) and continues the series of organo-metallic complexes of heterocycles. The present contribution covers a broad class of chelating ligands constituted by phosphinopyridines and related compounds. These interesting ligands possess both hard (pyridine nitrogen) and soft (phosphorus) coordination sites, which provides them with special properties in coordination chemistry. 

However, the reactivity of TJ toward insertion of small molecules into the Pd-Pd bond is much lower. Complex 1J does not insert carbon monoxide, sulfur dioxide or methyl isocyanide into the Pd-Pd bond. However, the pyridine nitrogen appears readily displaced. Thus 1J reacts with excess methyl isocyanide to form Pd2(CNCH3)i,(PPh2py)22+ and with carbon monoxide to form Pd2(C0)2-Cl2(PPh2py)2 (v(C0) at 2019 and 1994 cm-1)- These two products appear to contain monodentate, phosphorus-coordinated 2-diphenyl-phosphinopyridine and an intact Pd-Pd bond. 

Keywords Phosphorus Coordination / Donor-Acceptor Complexes / Structure... 

Compound 10 has been used for the preparation of chromium silylene (silandiyl) complexes containing coordinatively (and presumably also electronically) unsaturated Si [23]. Not surprisingly, in this complex an additional phosphorus coordination to silicon is observed (c (Si-P) = 2.380(1) A), whereby silicon expands its coordination number from three to four. 

The reactions of the phosphabenzene system [124] confirm these conclusions. Phosphabenzenes have low basicity towards hard acids. They are not protonated by CF3CO2H nor alkylated by trialkyloxonium salts. However, soft acids attack at phosphorus. For instance, 2,4,6-triphenyl-phosphabenzene forms compounds 4 with the hexacarbonyl derivatives of Cr, W and Mo in which the phosphorus coordinates to the metal, possibly with metal-P back-donation. The complexes 4 rearrange photochemically or thermally affording the 67i-heteroarene complexes 5. Although 2,4,6-triphenyl-pyridine is protonated on nitrogen, it undergoes complex formation with chromium hexacarbonyl exclusively on the phenyl moieties yielding the ri -arene complexes 6 [125]. 

Introduction - It is gratifying to report that interest in hypervalent phosphorus chemistry has been maintained, especially with regard to structural studies and the synthetic utility of pentaco ordinate phosphorus compounds. A novel departure has appeared in the area of hexaco-ordinate phosphorus with the synthesis of further phosphorus derivatives of the porphyrin ring system containing hypervalent phosphorus coordinated by the tetrapyrrole unit. The chapter will take its usual format, however, and the details of this small nugget will therefore appear in the last section. 

Similarly, the reactions of various cyclic P derivatives with diisopro-pylazodicarboxylate (DIAD) to achieve hypercoordination of phosphorus stemmed from the possibility of sulfur-phosphorus coordination. In one... 

NMR signal of Ic indicates that the phosphine functionality is not involved in the coordination to silicon, as was observed in pentacoordinate silicon phosphinomethanide complexes studied earlier by us [5]. Obviously, nitrogen coordination is preferred over phosphorus coordination despite the fact that in the latter case a five-membered ring may be formed instead of four-membered rings of the amidinate chelates. 

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