Carbonyls, matrix isolation studies

Matrix isolation studies on transition metal carbonyls and related species. J. K. Burdett, Coord. Chem. Rev., 1978, 27,1-58 (212). 

The elusive nature of binary gold carbonyls - known only from earlier matrix-isolation studies and from CO adsorbed on surfaces of bulk gold - has prompted quantum-chemical studies of the hypothetical species Au(CO) with n = 1, 2, 3. Two independent investigations (on the HF and ab initio level, MP2, CCSD(T)) have consistently... 

Matrix isolation studies usually permit spectroscopic observation of the species M(CO), M(CO)2,. M(CO) , the coordinatively saturated molecule. In some early studies, species thought to be simple unsaturated carbonyls were in fact carbonyls of metal clusters Mx(CO) a very low concentration of metal in the matrix (e.g., I mol in 104 mol noble gas) has to be used to prevent clustering. All the partially coordinated carbonyls are only matrix species, that is, they only exist when completely isolated from other molecules of their own kind or from CO. The coordinately saturated carbonyls are of more interest in the context of this review. The following new molecules have been reported Au(CO)2 (84a) Ag(CO)3, Cu2(CO)6 (46, 87) Pd(CO)4 (22), Pt(CO)4 (69) Rh2(CO)g, Ir2(CO)g (37) M(CO)6[M = Pr, Nd, Gd, Ho, Yb (100), Ta (24), U (117)]. The Cu, Pd, Pt, Rh, and Ir carbonyls can be obtained by condensing the metal vapors with pure CO at 40 K and then pumping off excess CO to leave a film of the carbonyl. The Cu, Pd, and Pt carbonyls decompose under vacuum temperatures above -100°C, and the Rh and Ir carbonyls dimerize with loss of CO to give M4(CO)12 above -60°C. The gold and silver carbonyls are not stable outside matrix isolation conditions. Unfortunately, the literature is presently unclear about the stability of the Ta and lanthanide hexacarbonyls outside a matrix. 

Gold(O) species containing carbonyl ligands have been identified (165, 166) in matrix-isolation studies involving gold atoms with carbon monoxide and dioxygen. 

Finally, matrix isolation studies have shown that the carbethoxysilene J (derived from the disilylcarbene I, equation 84), which rearranges to the disilylketene K by migration of the ethoxy group from the carbonyl-carbon atom to silicon, is the result of a photochemical process122. 

Two significant surveys are published in the sane edition of Coordination Chemistry Reviews. Oxygen donor-ligand derivatives of tri-osmium dodecacarbonyl are covered by Frauenhoff and the reactions of transition metal dihydrogen complexes (of which many are carbonyl-containing) are outlined by Jessop and Morris. The crucial role of matrix Isolation studies is well covered in this article. A shorter review of interest here has been published on the role of the phosphorus d-orbitals in M-P bonding. ... 

Before these matrix-isolation studies, it had been usual to denote carbonyl oxides as zwitterions cf. 48a), but the experimental IR spectra of 48 and its analogues did not exhibit absorptions that could be assigned to C=0 bonds. It was therefore concluded that carbonyl oxides are better represented as polar singlet biradicaloids cf. 48b). ... 

Nonmetal-atom, matrix-isolation spectroscopy has proved useful in structure and isomer determination of stable, metal carbonyls. Fe(CO)4(NO) was investigated (157) in low-temperature matrices with CO enrichment, and it was demonstrated that the IR spectrum is consistent with C v symmetry (trigonal bipyramid with an equatorial NO), in agreement with X-ray studies (55). The work resolves the dis-... 

Relatively little work has been done on the flash photolysis of gas phase metal carbonyls, partly because of the low volatility of many of the compounds. Early work by Callear (41,42) provided some evidence for Ni(CO)3 generated from Ni(CO)4 in the gas phase (41) and Fe atoms produced from Fe(CO)5 (42). This latter process has even been used as the basis of an Fe atom laser (43). More recently Breckenridge and Sinai (44) studied the flash photolysis of Cr(CO)6. Their results, interpreted largely on the basis of data from matrix isolation experiments, were in broad agreement with Kelly and Bonneau s solution work (JJ). In particular, they found no evidence for loss of more than one CO group [Eqs. (4) and (5)]. 

Spectroscopists also saw the potential of reacting ligands with transition metal under matrix isolation conditions. Photolysis of metal carbonyls in organic (383 or inert gas matrices (39) had already been done, but atoms offered the possibility of step-wise addition of ligands. DeKock (40), Turner (41 ), and Moskovits and Ozin (42) made early contributions, but the work of the last two became dominant (32). By 1972, there were the two distinct branches in transition metal atom chemistry, the preparative and matrix spectroscopic studies. 

In this section, we outline a number of studies by various workers in which matrix isolation experiments have contributed to the understanding of some photochemical pathways and where the objective was to relate the experiments to room-temperature photochemistry. We then consider briefly some current problems involving dinuclear and polynuclear carbonyls. 

Matrix isolation has already provided a valuable insight into the behavior of dinuclear carbonyls. In the first experiments of this kind we were able (Z2) to show that, on photolysis in solid Ar, Fe2(CO)9 loses CO to form Fe2(C0)g in both bridged and unbridged forms and the behavior of these fragments was studied ... 

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