David R. Saunders

Reactions of co-ordinated ligands. Part 36. The synthesis, structure, and reactivity of the three-alkyne ‘fly-over’ complex [Mo2{µ-(σ,η3:η3,σ-C6Me6)}(η5-C9H7)2]; formation and structure of [Mo2{µ-(σ,η3:η3,σ-C6Me6)}(CO)2(η5-C9H7)2]

One-electron reduction of [Mo(NCMe)(η2-McC2Me)2(η5-C9H7)][BF4] with sodium or magnesium amalgam in thf affords the three-alkyne ‘fly-over’ complex [Mo2{µ-(ση3:η3,σ-C6Me5)}(η5-C9H7)2](1). The structure of (1) has been established by X-ray crystallography. The dinuclear complex contains two molybdenum atoms at an interatomic distance consistent with the presence of a triple bond [Mo(1)–Mo(2) 2.305(2)A]. Each molybdenum carries an η5-bonded indenyl ligand, and is also bonded (σ and η3) to a C6Me5 fragment in a ‘fly-over’ mode beginning and ending with different molybdenum atoms. The mechanism of formation of (1) is discussed. It is interesting that (1) does not react with an excess of but-2-yne. However, treatment of the 30-electron species with CO at room temperature leads to the rapid formation of the 34-electron dicarbonyl species [Mo2{µ-(σ,η3:η3,σ-C6Me6)}(CO)2(η5-C9H7)2](2) whose structure was established by X-ray crystallography. The effect of the addition of two carbonyl ligands is to lengthen the Mo–Mo distance to 2.933(1)A, a length compatible with a bond order of unity. The increase in the Mo–Mo distance spanned by the C6Me5 fragment is accompanied by an uncoiling of the ‘fly-over’ unit. An isomeric dicarbonyl species (3) with higher symmetry (C2 instead of C1) is formed in refluxing hexane, suggesting that (2) is the kinetically controlled product. In contrast, 2,6-xylyl isocyanide reacts at room temperature with (1) to form [Mo2{µ-(σ,η3:η3,σ-C6Me6)}(CNC6H3Me2-2,6)2(η5-C9H7)2](4), which is isostructrual with (3), i.e. the thermodynamically controlled product. The formation of these molecules is discussed in the context of related species obtained on the thermal reaction of alkynes with the dinuclear complex [Mo2(µ-alkyne)(CO)4(η-C5H5)2].

C–C Bond formation and C–H bond cleavage in redox reactions of ruthenium complexes

Complexes [Ru(CO)2R1R2(PMe2Ph)2]decompose intramolecularly in CHCl3to yield ketines R1R2CO; the complex[Ru(Co)2(C6H4Me-4)2(PMe2Ph)2](1a) also yields [[graphic omitted])C6H4Me}Cl(PMe2Ph)2](4).

From diarylruthenium complexes to ortho-metallated ketones: a mechanistic and crystal structure study

In the presence of CHCl3, CCl4, or Etl, diary1 complexes [Ru(CO)2(C6H4Y-4)(C6H4Y′-4)L2](Y = Y′= Me, L = PMe2Ph or AsMe2Ph; Y = Y′= Cl, L = PMe2Ph; Y = Me, Y′= Cl, L = PMe2Ph) are converted in solution into products [R[graphic omitted])C6H4Y}XL2], where X = Cl or I. The structure of [R[graphic omitted])C6H4Me}Cl(PMe2Ph)2], complex (3a), has been determined by X-ray crystallography. The proposed mechanism involves a two-step combination of aryl and carbonyl ligands to give [Ru(CO){OC(C6H4Y-4)(C6H4Y′–4)}L2], followed by insertion of the metal into a C–H bond in one of the arene rings and reaction of the resulting hydrido-complex with the halogen-containing compound. Probably as a result of the stereochemistry of the insertion step, the product [R[graphic omitted])C6H4Y}XL2] is initially obtained as an isomer with mutually cis L ligands; this then rearranges to the isolated product with trans L ligands. The iodide ligand in the complex [R[graphic omitted])C6H4Me}I(PMe2Ph)2] can be displaced by Me3CNC, and the complete organic ligand in complex (3a) is transferred from ruthenium to mercury on treatment with HgCl2.

Phenyl complexes of ruthenium(II): competition between carbonyl substitution and formation of benzoyl complexes, and an X-ray study of a benzoyl complex

Complexes [Ru(CO)2(C6H4X-4)Y(PMe2Ph)2](X = H, Y = Cl, l, or O2CMe; X = OMe, Cl, or NMe2, Y = Cl) react with Me3CNC in CHCl3 solution to yield carbonyl substitution products [Ru(CO)(CNCMe3)(C6H4X-4)Y(PMe2Ph)2] and benzoyl complexes [Ru(CO)(CNCMe3)2-(COC6H4X-4)(PMe2Ph)2]+ in proportions which vary widely according to the conditions used and the nature of X and Y. The most probable route to the benzoyl complexes appears to be via intermediates of formula [Ru(CO)(CNCMe3)(COC6H4X-4)Y( PMe2Ph)2]. The structure of [Ru(CO)(CNCMe3)2(COPh)(PMe2Ph)2]I3 has been determined by X-ray crystallography.

Structure of a cis-dimetalla-alkene complex formed by the reaction of a ruthenium(II) complex with bis(phenylethynyl)mercury(II)

X-Ray investigation of the product of the reaction of trans-[Ru(CO)2Cl2(PMe2Ph)2] with Hg(CCPh)2shows it to be [Ru(CO)2{C(CCPh)C(Ph)HgCl}Cl(PMe2Ph)2]. The proposed mechanism involves formation on the ruthenium of 1,4-diphenylbuta-1,3-diyne, and cis addition of an Ru–HgCl bond across one of the triple bonds of the diyne. The mass spectrum of the complex indicates that this addition is reversed on heating, with release of the diyne. The related complex [Ru(CO)2{C(CCCMe3)C(CMe3)HgCl}Cl(PMe2Ph)2], prepared in the same way, decomposes slowly in solution even at room temperature, with release of Me3CCC-CCCMe3 and deposition of mercury.

Synthesis and interconversion of, and restricted rotation in, phenyl complexes of ruthenium(II)

The preparation and characterization of a range of phenyl complexes of ruthenium(II) are reported. For many of the complexes there is a substantial barrier to rotation of the phenyl ligand about the metal–phenyl bond, and n.m.r. studies have shown how the rate of rotation is affected by changes in the ligands in the complexes. Reaction of complexes [Ru(CO)(C6H4X)Y(PPh3)2] with phosphorus or arsenic ligands L provides a convenient route to [Ru(CO)(C6H4X)YL3][X = H, Y = Cl, L = P(OMe)3, PMe2Ph, PMePh2, P(OMe)2Ph, or AsMe2Ph; X = H, Y = Br or I, L = P(OMe)3; X = 4-MeO, 4-Cl, or 4-Me, Y = Cl, L = P(OMe)3]: 31P and 13C n.m.r. studies have demonstrated the sequence of steps involved and the stereochemistry of the intermediates, showing the influence of the trans-labilizing and trans-directing effects of the phenyl ligand.

Combination of aryl and carbonyl ligands in ruthenium(II) complexes: a kinetic study

Reactions of diaryl complexes [Ru(CO)2RR′(PMe2Ph)2] with Me3CNC yield the acyl complexes [Ru(CO)(CNCMe3)(COR)R′(PMe2Ph)2]. Rate-determining combination of aryl and carbonyl ligands is followed by rapid attack by isonitrile trans to the acyl ligand. In symmetrical diaryl complexes, rates are increased by electron-releasing substituents in the para position of the aryl ring. A methyl substituent in the meta position has a rather large accelerating effect, presumably for steric reasons. In unsymmetrical diaryl complexes, the aryl ligand bearing the more electron-releasing substituent becomes incorporated in the acyl ligand. Variations in the aryl ligand not directly involved in the reaction have little effect on rate, and solvent effects are relatively small. The fairly large negative entropies of activation are attributed to the formation in the transition state of a three-membered metal–carbonyl–aryl ring, in which the aryl ring has presumably lost its freedom of rotation.

Kinetics of the combination of methyl ligands with carbonyl or isonitrile ligands in ruthenium(II) complexes

Methyl complexes [Ru(CO)2MeR(PMe2Ph)2][(1a), R = Ph; (1b), R = COMe; (1c), R = Me] react with Me3CNC to form acetyl complexes [Ru(CO)(CNCMe3)(COMe)R(PMe2Ph)2], (2a)–(2c). The reaction rate is independent of isonitrile concentration, and the rate-determining step is believed to involve combination of methyl and carbonyl ligands. The reactions of complexes (1b) and (1c) are similar both in rate and in activation parameters, but for (1a)ΔH‡ is appreciably lower and S‡ more negative: this may be due to increasing Ru–Ph π bonding in the approach to the transition state. Complex (2c) reacts with more Me3CNC to form [Ru(CO)(CNCMe3)(COMe){C(NCMe3)Me}-(PMe2Ph)2], (3c). Here the rate-determining step appears to involve combination of methyl and isonitrile ligands; this is much slower than combination of methyl and carbonyl ligands owing to a more negative ΔS‡. In the absence of added Me3CNC, complex (2c) slowly disproportionates into (1c) and (3c).

Reductive elimination of ketones from ruthenium(II) complexes

Complexes [Ru(CO)2R2(PMe2Ph)2](R = aryl or alkyl) decompose at room temperature in CHCl3 or Me2CO solution to yield the ketones R2CO. Decomposition is intramolecular, since the complexes [Ru(CO)2RR′(PMe2Ph)2] yield only the unsymmetrical ketones RR′CO, and the disappearance of [Ru(CO)2(C6H4Me-4)2(PMe2Ph)2] follows simple first-order kinetics. The acyl complex [Ru(CO)(CNCMe3)(COC6H4Me-4)(C6H4Me-4)(PMe2Ph)2] also decomposes in CHCl3 solution to give (4-MeC6H4)2CO, but the decomposition is inhibited by free Me3CNC. It is believed that the ketones are formed by reductive elimination from [Ru(CO)(COR)R(PMe2Ph)2]. A ruthenium(0) product could not be isolated, but the ruthenium(II) complex [[graphic omitted]C6H4Me}(PMe2Ph)2] was obtained when the decomposition of [Ru(CO)2(C6H4Me-4)2(PMe2Ph)2] in CHCl3 was carried out at higher temperatures.

Dialkyl, diaryl, and alkyl aryl complexes of ruthenium(II)

Whereas HgR2(R = methyl or aryl) converts trans-[Ru(CO)2Cl2(PMe2Ph)2] exclusively into [Ru(CO)2R(Cl)(PMe2Ph)2] and does not react with cis-[Ru(CO)2Cl2(PMe2Ph)2], LiR reacts with either isomer to yield [Ru(CO)2R2(PMe2Ph)2] and also catalyses conversion of the trans isomer into the cis. The initial attack by R– is believed to be on a carbonyl ligand. Treatment of [Ru(CO)2R(Cl)(PMe2Ph)2] with LiR′ yields mixed complexes [Ru(CO)2R(R′)(PMe2Ph)2]. In all cases the two organic ligands are mutually cis. The dimethyl complex undergoes reversible carbonylation to form mono- and di-acetyl complexes, and [Ru(CO)2Me(Ph)(PMe2Ph)2] also forms an acetyl complex, but aryl ligands are unaffected by treatment with CO.