The reaction of Schiff bases of 2,6-diformyl-4-methylphenol with M(PPh3)3X2 in ethanol has afforded carbonylhalo[4-methyl-6-(N-R-iminiomethyl)phenolato-C 2,O]bis(triphenylphosphine)metal(II) compounds, MII(RL)(PPh3)2(CO)X (M = Os, X = Br; M = Ru, X = Cl; R = alkyl, aryl). The process is believed to proceed via oxidative addition of the aldehydic C(O)−H bond to the metal followed by CO extrusion and reductive proton elimination. The X-ray structure of Os(EtL)(PPh3)2(CO)Br·CH2Cl2 has revealed the presence of the distorted octahedral OsC2P2BrO coordination sphere. In the four-membered, Os(C,O) chelate ring, the metal atom is bonded to the carbon site to which an aldehyde group was attached in the parent ligand. The presence of the iminium−phenolato zwitterionic motif is consistent with the N···O length as well as with IR and 1H NMR spectra. Bond parameters of the osmium and ruthenium systems are compared. Significant dπ−pπ back-bonding with the metalated aromatic ring occurs in the case of osmium. The complexes display a quasi-reversible one-electron cyclic voltammetric couple (E 1/2 = 0.50−0.70 V), but the oxidized congeners are too unstable to be isolated. Upon reaction of M(RL)(PPh3)2(CO)X with carboxylates, the latter gets chelated, the M−O(phenolato) linkage is cleaved, and the iminium−phenolato function tautomerizes to the imine−phenol function.

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Ruthenium(II) Phenolates. Synthesis and Characterization of A Novel Four-Membered Metallacycle Ruthenium phenolates constitute a small family of interesting complexes.1 While 4-methy!-2,6-diformylphenol (1) was studied as a potential binucleating ligand for the metal, complexes of composition Ru(/?-XC6H4L)(CO)(PPh3)2Cl, incorporating 2, were discovered. The X = Me complex 3, described here, is representative of the family.2 Reaction of Ru(PPh3)3Cl2 (100 mg, 0.10 mmol), 1 (26 mg, 0.15 mmol), and p-MeC6H4NH2 (17 mg, 0.15 mmol) in boiling ethanol (30 mL) for 0.5 h (the reaction does not proceed in the absence of the amine) affords a violet solution, which, upon cooling, deposits 3 as dark violet crystals in nearly quantitative yield.3 The same results are obtained when 1 + />MeC6H4NH2 is replaced by an equivalent amount of the preformed Schiff base 4 (40 mg, 0.15 mmol), which is thus the active reagent in the synthesis. Benzene can replace ethanol as the solvent without loss of synthetic efficacy.The X-ray structure4,5 of 3 is shown in Figure 1. The ru-

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Decarbonylative metallation of the dialdehyde 2b by [Ru(PPh3j3Cl2] affords the unusual complex [Ru(MeL)(C0)(PPh3),(Cl)] 4 which has been characterised by X-ray crystallography and in which the RullP2C2CI0 coordination unit bears a single net negative charge; the Ru(MeL) (3, R = Me) fragment incorporates a four-membered C,O-chelated phenolato function with a neigh bouring monoprotonated azomethine moiety.