Dihydrogen coordination

These species could only be studied spectroscopically, but we now had stable analogues that could be studied crystallographically. A series of 16e M(CO)3(PR3)2 

The syntheses of M(CO)3(PR3)2 succeed only for bulky phosphines and, curiously, only for P Pr3 and PCy3 whereas similar-sized phosphines such as P Bu3 do not work. By good fortune I had chosen the only reaction and the only reactants 

X-ray diffraction studies of ( ) ( 3)2( 2) produced only frustration because crystallographic disorder prevented location of hydrogen positions. This 

Speculation over our provocative findings continued for months, especially after they were prematurely reported in a C E News article in April 1983, highlighting new findings at the Seattle ACS meeting. We had not yet submitted a paper on our 

Although a large degree of disorder was still present in the C-H positions of one of the P Pr3 ligands (which hindered publication of the structure), the side-on bonded H2 ligand was seen clearly with a dm of 0.82 A. As mentioned in Chapter 1 and as will be discussed further on, tautomeric equilibrium of W(CO)3(PR3)2(H2) with its dihydride form was soon found and elegantly demonstrated that H2 complexes are true intermediates in the OA of H2.25 

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Fig. 3. Creation of the open site and dihydrogen coordination. The energies indicated are relative to F0(l) + E0(H2) = 0 and are given in kcal mol-1. (Species corresponding to 5, 6, and 11 were not located.)...

Just as bridging hydrides play a central role in the chemistry of Group 13 hydrides, three centre-two electron (3c-2e) bonding is a recurrent fea- Figure 2.17 Polyhydride vs ture of binuclear (and polynuclear) hydrides of the transition metals dihydrogen coordination... 

Figure 2.22 Synergic bonding in dihydrogen coordination hydrogen to metal donation and metal to hydrogen retrodonation...

Cis-H2Pt[Men(Ph)P(CH2)2P(Ph)Men] (Men = 1-menthyl) and cis-H2Pt[(t-Bu)-(Ph)P(CHj)2P(Ph)(Bu-t)] are prepared from the corresponding PtCl2(diphos) complex by reduction with Na/Hg (1%) in THF under Hj. These two complexes are stable crystalline solids, and the dihydrogen coordination is reversible in solution. 

THEORETICAL STUDIES OFM(C0)3(PR3)2(H2) AND BONDING MODEL FOR DIHYDROGEN COORDINATION... 

H-H DISTANCE AND OTHER CRYSTALLOGRAPHIC AND STRUCTURAL ASPECTS OF DIHYDROGEN COORDINATION... 

The reversible reaction of with complex 6 has been proposed to involve dihydrogen coordination to an equatorial position of the Ir(II) center, followed by single-metal addition and hydride migration steps. The axial-to-equatorial movement of the coordination vacancy required by this mechanism has been shown to be a facile process. 

The stereochemistry of the reaction products of Scheme 7 again suggests that these reactions involve single-metal additions preceded by dihydrogen coordination to equatorial positions. In this respect, it has been shown that complex 9 can readily dissociate its acetonitrile ligands, and exchange them from axial to equatorial positions with low kinetic barriers.[28] Such vacancy rearrangements... 

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