Isostructural carbonyl complexes

Matrix-isolation techniques permit the isolation of Pd(CO)4 in a CO matrix. This imstable species exhibits a vco of 2066 cm . The analogous Pt(CO)4 gives vco of2044cm and the vco of Ni(CO)4 is 2037 cm. The increase in vco is further indication that d -p r bonding decreases in the order Ni > Pt > Pd. In general, platinum carbonyls have a lower vco value than isostructural palladium complexes. 

Before it is possible to interpret on a rigorous basis the behavior of the carbonyl stretching frequencies of a series of isostructural and isoelectronic complexes complete vibrational analyses are necessary. However, it is only within the last few years that far-infrared 137) and laser Raman 84) spectrometers have become available generally. Hence, in the general absence of the data they have provided, earlier complete analyses were limited to the spectra of simple metal carbonyls (for which such information was available). Even for these complexes, the number of force constants exceeds the number of observable frequencies, and model force fields had to be used. Since Urey-Bradley type force fields proved to be unsuitable for carbonyl complexes 86,105, 106), Jones 80-82) developed a resonance interaction valence force field which reduced the number of force constants by interrelating several on the basis of orbital overlap. This approach is not readily adaptable to less symmetrical substituted carbonyl complexes. Alternative models had, therefore, to be investigated. 

Fifth, the rate of carbonyl insertion as a function of the metal center usually follows the trend 3d > 4d > 5d when the complexes are isostructural. Alkyl complexes of the first-row metals are almost always more reactive than the analogs of the third row, and they are usually more reactive than the analogs of the second row. For example, CpRu(CO)jMe requires higher temperatures to insert CO in the presence of added phosphine than does the analogous iron complex, and the osmium analogue fails to react. Similar trends have been observed for other alkyl complexes of metal-carbonyl fragments. For CpM(CO)jR complexes, the relative rates of insertion are M = Cr and Mo > W, and for RM(CO)j, the relative rates are M = Mn >... 

Both the indium and gallium clusters E4 G(TMS)3)4 (E = Ga, In) react with 2 equiv. of [NiGp(GO)]2 to give the bis(/i-EG(TMS)3)-substituted complexes, [Ni(GO)Gp]2 /x-EG(TMS)3 which are isostructural with the starting carbonyl complex. Quantum chemical calculations support the view that there are no In-In or Ga-Ga bonding interactions in the butterfly structure complexes, Ni / -EG(TMS)3 Gp2. 

Hence it is more appropriate to view noble-metal carbonyls and their derivatives as coordination complexes of CO rather than as organometallic compounds. A comparison to metal cyanide complexes is far more appropriate, in particular since [Au(CO)2]+ and [Au(CN)2] as well as [Pt(CO)4]2+ and [Pt(CN)4]2- are isoelec-tronic and isostructural pairs. Strong bonding similarities have been established for the first pair (9). It is unlikely that cationic metal-carbonyl complexes will ever form so many different species as the cyanide complexes, which are known for most transition metals (86). With useful and facile synthetic routes available, further examples of cationic metal carbonyls with similar bonding and spectroscopic features as described here should be prepared and characterised in the future. 

Coordination chemistry of ER The monomeric fragments E-R are isolobal to carbon monoxide, and many complexes analogous to transition metal carbonyls have been synthesized (41 to 43, see Figure 2.3-7) [68], In most cases these reactions started with those clusters which have a high tendency to dissociate and to form monomers, such as pentamethylcyclopentadienylaluminum(I) or the alkylgal-lium(I) or alkylindium(I) derivatives. Often the products are isostructural to the respective metal carbonyls, but exceptions are the gallium compounds 44 and 45. 

Tricobalt clusters with one triply bridging ligand, isostructural with 65, have been extensively investigated. The carbonyls [Co3(CO)9(/u-E)] (72) (E = S, Se, or PR) have one electron in excess of that required for an 18-electron configuration about each metal. The half-filled orbital is antibonding with respect to the metal triangle (144, 145), and the complexes are easily oxidized (see also, Section IV,B). 

The stabilities of the metal-carbon bond formed from oxidative additions are as varied as their mechanistic pathways. Metal-carbon bond strengths increase going down a triad in an isostructural series of complexes. Alkyl migration to CO ligands on the metal to form acyl derivatives is more facile in first-row transition metals because of their lower metal-carbon bond energies. The thermal stability of alkyls vs. acyls does not follow any pattern, except that the availability of a sixth coordination site in ML (acyl) complexes favors the alkyl carbonyl isomer. The corresponding acyl, which can be made by running the reaction of the alkyl or aryl halide in CO (at 1-3 atm), is more stable by... 

Three of the four-coordinate metal nitrosyl complexes of the isoelectronic and isostructural Ni(CO)4 series, Mn(NO)3(CO), Fe(NO)2(CO)2, and Cr(NO)4, are formed when respective binary metal carbonyl solutions (n-pentane, cyclohexane) are irradiated in the presence of a slow stream of The... 

These complexes are isoelectronic and isostructural with the bis-phosphine Ir carbonyl chloride complex, but they differ in two respects (a) the reaction with is irreversible and (b) the oxidative addition of yields three different cis isomers as a result of a solvent dependence for this addition. The complexes trans-CPR ROjIrCCOftr-carb) (R = CjHj R = CgHj, CHj) react with or D, giving the (PR ROjIrH (or D ) (CO)((T-carb) dihydrides or dideuterides. These complexes are colorless crystalline compounds, nonelectrolytes in solution and stable with respect to thermal loss of either carborane or H, however, they are light sensitive. 

The two isostructural clusters [Co6N(CO)i5] and [Rh6N(CO)i5] were synthesized by reaction of the octahedral clusters [M6(CO)i5] (M = Co, Rh) with nitrosonium tetrafluoborate. Better yields of the rhodium species were obtained by treatment, in a strongly reducing medium, of [RhyjCOjie] " with NO (diluted 1 1 with CO). The reactions are complex and no intermediate step could be identified. However, a nitrosyl derivative is very likely to be involved, and subsequent reduction, by the reaction medium or the starting reduced carbonyl itself, would yield the nitrido cluster. 

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