Isocyanide complexes of ruthenium

Abstract

A study has been made of ruthenium isocyanide complexes. The isocyanide used was p-tolylisocyanide, although some complexes of p-anisyl, p-chlorophenyl- and p-nitrophenylisocyanides were also prepared. Particular attention was focussed on zerovalent isocyanide complexes, and carbene complexes derived from isocyanide-containing precursors. (a) Divalent Ruthenium Isocyanide Complexes Divalent ruthenium hydrido-isocyanide complexes were prepared as starting materials. The complex RuHCl(CO)(CNR)(PPh3)2, obtained from the reaction of isocyanide with RuHCl(CO)(PPh3)3, with silver perchlorate affords RuH(OClO3)(CO)(CNR)(PPh3)2. The labile perchlorato group is easily replaced by anions to give neutral complexes of the type RuHX(CO)(CNR)(PPh3)2 (X=Cl, I, SSCNEt2, SSCNMe2) and by neutral molecules to give the cationic products, [RuH(CO)(CNR)(L)(PPh3)2]ClO4 (L=CO, CNR, tertiary arylphosphine, phosphite and CH3CN). Substitution of a triphenylphosphine ligand in RuH2(PPh3)4 by neutral molecules gives the complexes RuH2(L)(PPh3)3 (L=CO, CNR, phosphite). Hydride cleavage from the dihydride complexes by carboxylic acids gives the compounds, RuH(R’COO)(L)(PPh3)2. (L=CNR, PPh3, phosphite; R’=Me, Ph, p-tolyl). The reaction of three equivalents of isocyanide or phosphite with RuH(R’COO)(PPh3)3, in the presence of sodium perchlorate, affords the cationic complexes [RuH(L)3(PPh3)2]ClO4 (L=CNR, phosphite) while two equivalents of isocyanide give trans-[RuH(CNR)2(PPh3)3]ClO4. The complex cis-[RuH(CNR)2(phosphite)(PPh3)2]ClO4 is prepared similarly from RuH(R’COO)(phosphite)(PPh3)2. (b) Zerovalent Ruthenium Isocyanide Complexes Formal deprotonation of the cationic complexes cis-[RuH(CO)2(CNR)(PPh3)2]ClO4, cis-[RuH(CO)(CNR)2(PPh3)2]ClO4, [RuH(CO)(CNR)(PPh3)3]ClO4 and trans-[RuH(CNR)2(PPh3)3]ClO4 with ethoxide ion gives the d8 complexes Ru(CO)2(CNR)(PPh3)2, Ru(CO)(CNR)2(PPh3)2, Ru(CO)(CNR)(PPh3)3 and Ru(CNR)(PPh3)3, respectively. Protonation of these zerovalent ruthenium compounds with non-coordinating acids, or reaction with mercuric halides, gives cationic products, exclusively. However, protonation with coordinating acids and halogenation gives cationic complexes with Ru(CO)2(CNR)(PPh3)2 and Ru(CO)(CNR)2(PPh3)2, but neutral products with Ru(CO)(CNR)(PPh3)3. In addition, Ru(CO)(CNR)(PPh3)3 forms adducts with small molecules like dihydrogen, carbon disulphide and dioxygen. A chelated carbonate complex viz., Ru(CO3)(CO)(CNR)(PPh3)2, is isolated from the reaction of Ru(CO2)(CNR)(PPh3)2 with dioxygen. While chlorination of Ru(CNR)2(PPh3)3 also gives a neutral product, viz., cis-RuCl2(CNR)2(PPh3)2, reaction with bromine or iodine led to the isolation of unsaturated, d6, cationic complexes, trans-[RuX(CNR2)(PPh3)2]X3 (X=Br, I). (c) Hydride Transfer The reaction of carbon monoxide with RuH(R’COO)(CNR)(PPh3)2, at room temperature, produces the formimidoyl complex Ru(CHNR)(R’COO)(CO)(PPh3)2, by hydride to isocyanide migration. Further reaction with dialkyldithiocarbamate ions gives the complexes Ru(CHNR)(SSCNR’2)(CO)(PPh3)2 (R’=Me, Et) while isocyanide opens the carboxylate ring to give Ru(CHNR)(R’COO)(CO)(CNR)(PPh3)2. The analogous complex, cis-Ru(CHNR)(R’COO)(CNR)2(PPh3)2 is obtained in a one-step reaction between RuH(R’COO)(CNR)(PPh3)2 and isocyanide. Hydride migration, from the formimidoyl group back to the metal, to give RuHI(CO)(CNR)(PPh3)2 (H trans CO), is observed in the reaction of Ru(CHNR)(R’COO)(CO)(PPh3)2 and iodide ions. Subsequent reaction of RuHI(CO)(CNR)(PPh3)2 (H trans CO) with diethyldithiocarbamate ions returns a formimidoyl complex, viz. Ru(CHNR)(SSCNEt2)(CO)(PPh3)2. (d) Carbene Complexes Carbene complexes have been prepared by protonation or methylation at the nitrogen atom of the formimidoyl group. Ru(CHNR)(R’COO)(CO)(PPh3)2 (R=Me, Et) and Ru(CHNR)(SSCNEt2)(CO)(PPh3)2 are reversibly protonated by perchloric acid to give [Ru(CHNHR)(R’COO)(CO)(PPh3)2]ClO4 and [Ru(CHNHR)(SSCNEt2)(CO)(PPh3)2]ClO4, respectively. Coordinating acids give the neutral products RuX2(CHNHR)(CO)(PPh3)2 (X=Cl, Br, CH3COO, PhCOO). The complexes [Ru(R’COO)(CHNHR)(CO)(CNR)(PPh3)2]ClO4 (R’=Me, Ph, p-Me.C6H4) have been prepared. The monodentate carboxylate group is replaced by the covalent perchlorate group, using perchloric acid, at 80°C. The complex cis-[Ru(OClO3)(CHNHR)(CNR)2(PPh3)2]ClO4 is prepared similarly from the action of perchloric acid on cis-Ru(CHNR)(R’COO)(CNR)2(PPh3)2. Substitution of the perchlorato group by carbon monoxide or isocyanide affords the doubly-charged cationic carbene complexes, cis-Ru(CHNHR)(CO)2(CNR)(PPh3)22, cis-Ru(CHNHR)(CO)(CNR)2(PPh3)22 and mer-Ru(CHNHR)(CNR)3(PPh3)22. The majority of these complexes exhibit a significant C(carbene)-H/N(carbene)-H interaction in their 1H n.m.r. spectra. Methylation of Ru(CHNR)(R’COO)(CO)(PPh3)2, in the presence of sodium perchlorate, produces [Ru(R’COO){CHN(Me)R}(CO)(PPh3)2]ClO4. Reaction of the latter with chloride ions gives RuCl2{CHN(Me)R}(CO)(PPh3)2. A chloride group in this complex is easily replaced by formate ions or by carbon monoxide, in the presence of sodium perchlorate, to give RuCl(HCOO){CHN(Me)R}(CO)(PPh3)2 and cis-[RuCl{CHN(Me)R}(CO)2(PPh3)2]ClO4, respectively. The complex [Ru(R’COO){CHN(Me)R}(CO)(CNR)(PPh3)2]ClO4, prepared by methylating Ru(CHNR)(R’COO)(CO)(CNR)(PPh3)2, reacts with perchloric acid at 80°C to give [Ru(OClO3){CHN(Me)R}(CO)(CNR)(PPh3)2]ClO4. As above, reaction with carbon monoxide or isocyanide leads to the isolation of doubly-charged cationic carbene complexes, viz. cis-Ru{CHN(Me)R}(CO)2(CNR)(PPh3)22 and cis-Ru{CHN(Me)R}(CO)(CNR)2(PPh3)22. Methylation of Ru(CHNR)(R’COO)(CO)(CNR)(PPh3)2, followed by reaction with excess iodide ions at 90°, gives the neutral mono-phosphine complex RuI2{CHN(Me)R}(CO)(CNR)(PPh3).