Dinuclear carbonyls preparation

The reaction of RhHL3 (L = P(iso-Pr)3) with CO was thought to give Complex 7. Instead, the product formed from the reaction in dry hexane under a CO atmosphere was a binuclear Rh(0) carbonyl compound, Rh2(CO)3L3 (Complex 8, IR v(CO) 1732, 1768, and 1957 cm"1) (12). The similar reaction of RhHL3 containing bulkier phosphines produced Rh2(CO)4L2 (L = P(cyclo-CeHii)3, PPh(f-Bu)2, P(f-Bu)3). These dinuclear carbonyl compounds can be prepared by treating trans-RhH(CO)L2 with CO at room temperature. The formation of Rh2(CO)3L3 requires several steps, and a plausible sequence is proposed below. 

Again starting from the decacarbonyl dimetalate(-I) anions, besides the mononuclear [M(CO)sX] anions, we were the first to prepare the dinuclear [M2(CO)toX] species (M = Cr, Mo, W) with the respective metal having the oxidation state 0. These anions can be formally derived from the unknown dinuclear carbonyls M2(CO)n by substituting a CO ligand by X" (X = CN, I, NCS, SH, SMe, SEt, SPh). 

The mono- and dinuclear carbonyl metalates of Cr, Mo, and W, first prepared by us using liquid NHS, have also been of great importance for the synthesis of numerous neutral complexes not accessible by other routes. Special attention is drawn to the deeply colored and very unstable mono- and dinuclear paramagnetic complexes Cr(CO)sI, Cr (CO),oI, Cr(CO)5CN, Cr(CO)sNCS, Cr COl.oNCS, and Cr(CO)sSH. 

The existence of [Rh2( 0)8] under normal conditions has not been confirmed, although its synthesis from dispersed metal under pressure (28 MPa) and at 473 K had been reported. However, it was shown that [Rh2( 0)8] exists in solutions only at high pressures and at low temperatures.[Rh2(CO)8] and [Ir2( 0)8] were also prepared by reactions of atomic Rh and Ir with carbon monoxide in 0 matrices. During condensation at 10 K, [Rh( 0)4] or [Ir( 0)4] are formed first, and subsequently at 50 K react to give [M2( 0)8] compounds. At 223 K, the dinuclear carbonyls are transformed into [M4( 0)i2]. This means that with respect to tetranuclear compounds, the dinuclear complexes are thermodynamically unstable. [Rh2( 0)8] in solutions as well as in the matrix and [Ir2( 0)8] in the matrix have bridging carbonyl groups (Table 2.26). 

Stable, dinuclear carbonyls of this group are not known. The reason for this is the too low energy of [n— )d orbitals and too high energy of np orbitals (as in the case of Pd and Pt). Nevertheless, many metal carbonyls of group 11 metals were prepared by condensation of metal atoms with carbon monoxide at temperatures ca 15 K [M(CO)], [M(C0)2] where M = Cu, Ag, and Au, [M(CO)3], and [M2(CO)6] where M = Cu and Ag. These compounds have ooh 3 symmetries, respec-... 

Preparation of Dinuclear Carbonyls from Mononuclear Carbonyls... 

The first homoleptic, dinuclear platinum(I) carbonyl complex [Pt2(CO)6]2+ has been prepared by dissolving Pt02 in concentrated sulfuric acid under a CO atmosphere.92,93 The structure is rigid on the NMR time scale at room temperature. DFT studies suggested a staggered structure for the dimer.92,93... 

Electrochemical reduction of mononuclear binary carbonyls on the preparative timescale generally leads to CO loss and the formation of dinuclear dianionic products. For example, M(CO)6 (M = Cr, Mo, or W) undergoes irreversible electrochemical reduction near —2.7 V versus SCE in tetrahydrofuran (THF) containing [NBU4][BP4]. The product of the reductions are the dinuclear dianions [M2(CO)io] [14, 21], although under some conditions... 

Figure 7 The preparations and crystal structures of copper(I) carbonyl (a) mononuclear and (b) dinuclear complexes...

Bis[iV,iV -di(2-pyridyl)-imidazol-2-ylidene]aurate(I) tetrafluoroborates, preparation, 2, 292-293 Bis[iV,iV -di(2-pyridyl-methyl)-imidazol-2-ylidene]aurate(I) tetrafluoroborates, preparation, 2, 292-293 Bis(diselenolate) complexes, dinuclear iron compounds, 6, 242 Bis(dithiolene) compounds, in tungsten carbonyl and isocyanide complexes, 5, 644 Bis(enolato) complexes, with bis-Cp Ti(IV), 4, 589 Bis(enones), in reductive cyclizations, 10, 502 Bis(ethanethiolato) complexes, with bis-Cp Ti(IV), 4, 601 Bis(ethene)iridium complexes, preparation, 7, 328-329 -Bis(fluorenyl)zirconocene dichlorides, preparation,... 

Diphosphaferrocene, with chromium carbonyls, 5, 220 l,l -Diphospha[2]ferrocenophane, synthesis, 6, 210 Diphosphazanes, in dinuclear Ru complexes, 6, 674 l,l -Diphosphetanylferrocenes, preparation, 6, 200-201 Diphosphine borane complex, polypyrrole support for,... 

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