Joyce E. Shade

Photochemistry of some iron and ruthenium (η5-cyclopentadienyl) carbonyl dimers in frozen gas matrices at ca. 12 K

The photochemistry of [M2(η5-C5H5)2(CO)4][M = Fe, (1); or Ru, (2)] and [CH2{(η5-C5H4)M(CO)2}2][M = Fe, (5); or Ru, (6)] has been studied in frozen-gas matrices (Ar, CH4, and N2) at ca. 12 K and that of (2) in poly (vinyl chloride)(pvc) films at ca. 12 K. Low-energy photolysis of compounds (1) and (2) was found to induce opening of trans-carbonyl-bridged species affording terminal carbonyl species. Photolyses into the electronic absorption band maxima of these new terminal-carbonyl species yielded 17-electron radical species [M(η5-C5H5)(CO)2]˙ as well as small amounts of triply carbonyl-bridged species, [M2(η5-C5H5)2(µ-CO)3]. At the corresponding maxima of trans-carbonyl-bridged complexes (1) and (2) photolysis yielded the triply-carbonyl-bridged species directly. Photolysis of (5), which is exclusively bridging and is constrained by the methylene linkage between the rings to be in a cis conformation, at a range of wavelengths showed no evidence for carbonyl-bridge opening. At its electronic absorption maxima photolysis resulted in carbonyl ejection and formation of a new species whose spectrum is consistent with its having three terminal carbonyl groups and an Fe–Fe double bond. Photolysis of compound (6) which exists in a cis-terminal conformation also resulted in carbonyl loss and formation of a species similar to that observed for (5). These results are discussed in terms of their relationship to previous photochemical studies of (1) and (2) and an overall model for the photochemical behaviour of (1) and (2) is presented.

Structural and rotational isomerism in diaminocarbene complexes of iron

Abstract Primary amines react with a variety of cationic and neutral iron isocyanide complexes to yield structural and rotational diaminocarbene isomers characterized by variable temperature 1H and 13C NMR spectra. Structural isomers result from the conversion of amines to isocyanide ligands via the base-catalyzed nucleophilic attack of initially formed diaminocarbenes on cis isocyanides substituents, the effect on isomer populations is often marked. Factors influencing structural and rotational isomeric preferences are discussed.

Trisubstituted diaminocarbene complexes of iron

Abstract Neutral and cationic isocyanide complexes of the form CpFe(CO)(L)(CNR) where L = CN or CNR and R = Me or i-Pr react with dimethylamine to form trisubstituted diaminocarbenes. Secondary amines having larger alkyl groups were unreactive under the same conditions. The new complexes are characterized by their infrared, 13 C and 1 H NMR spectra. In contrast to dialkyl diaminocarbenes, these compounds exist totally in one isomeric conformation, exhibit significantly lower C-N rotational barriers, and readily revert to their isocyanide precursors.

Two Monomeric Ruthenium Complexes Containing Bidentate Bis(diphenylphosphino) Ligands

The crystal structures of chloro(η 5 -cyclopentadienyl)[methylenebis(diphenylphosphine-P)]ruthenium-chloroform (1/1), [RuCl(C 5 H 5 )(C 25 H 22 P 2 )].CHCl 3 , (A), and chloro(η 5 -cyclopentadienyl) [1,2-ethanediylbis(diphenylphosphine-P)]ruthenium-chloroform (1/1), [RuCl(C 5 H 5 )(C 26 H 24 P 2 )].CHCl 3 , (B), are reported. Both complexes contain a central ring structure in which a pair of P atoms, linked by a -CH 2 - [in (A)] or a -C 2 H 4 - [in (B)] group, are bonded to a central Ru atom. The P-Ru-P bond angle undergoes expansion from 72.07 (2)° in (A) to 83.48 (2)° in (B). The bond distances around the Ru center are compared with values reported for similar compounds. Both structures include a chloroform solvent molecule in addition to the ruthenium complex. The chloroform molecule in (A) was found to be disordered.

The synthesis and characterization of mixed isocyanide complexes of cyclopentadienyliron

Abstract The alkylation of η5-C5H5Fe(CO)(CN)(CNR) complexes with primary, secondary, and tertiary alkyl iodides, R′I (R ≠ R′) produces the mixed isocyanide species [η5-C5H5Fe(CO)(CNR)(CNR′)]I. Infrared and NMR spectra of the new complexes are dischased. The effect of metal coordination on the 13C spectra of cationic and neutral isocyanide complexes is considered. The use of the chiral alkyl iodides, secbutyliodide and α-phenylethyliodide, results in configurationally non-labile diastereomers which, in the case of compounds of the latter, can be detected by 1H and 13C NMR spectra.

Photochemical reactions of bis(bistrimethylsilylamido)tin(II) with; Hexacarbonylmolybdenum and tungsten

Abstract Irradiation of M(CO)6 (M = Mo. W) and Sn[N(SiMe3)2]2 in hexane with UV light results in carbonyl substitution to form both M(CO)5Sn[N(SiMe3)2]2 and M(CO)4Sn[N(SiMe3)2]2)2 complexes. The M(CO)4L2 species present the first examples in which both cis and trans isomers have been observed upon substitution of bulky divalent main group IV ligands. The highly air-sensitive W(CO)5L and W(CO)4L2 complexes have been isolated.

Photochemistry of some manganese and chromium dinuclear metal carbonyl complexes in frozen gas matrices at ca. 12 K

Infrared spectroscopic evidence is presented to show that photolysis of the non-metal–metal bonded dimers [Mn2(µ-η5:η5′-C10H8)(CO)6], [Mn2(µ-η5:η5′-C5H4CH2C5H4)(CO)6], [Cr2(µ-η6:η6′-C12H10)(CO)6], and [Cr2(µ-η6:η6′-C14H14)(CO)6] together with its mononuclear analogue [Cr(η6-C7H8)(CO)3] in gas matrices at ca. 12 K results in CO ejection to yield [M(CO)2] molecular fragments rather than detachment of polyene rings or the formation of new M–M linkages via M–M bonding and/or CO bridging. The reactivity of the resultant [M(CO)2] molecular fragments is demonstrated by the recombination with CO when matrices (Ar, CH4) were irradiated with light of a longer wavelength and by the reactions with N2 and 13CO (5% in Ar or CH4) to afford [M(CO)2(N2)] and [M(12CO)n(13CO)3 –n] fragments, respectively. The failure to form new M–M linkages is attributed to the isolation of the dimers in pseudo-trans configurations in the matrix cages such that even the excess photochemical energy is insufficient to both cleave M–CO bonds and supply the energies required to rotate the bulky fragments in the rigid matrix cages. These findings are discussed in relation to solution photochemical reactions.