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A series of metallacumulenylidene complexes of the cycloheptatrienyl molybdenum auxiliary [Mo{(C) n CR2}L2(η-C7H7)]+ (n = 0−2; L2 = P-donor ligand) have been synthesized by reaction of [MoXL2(η-C7H7)] (X = Br, L2 = Ph2PCH2CH2PPh2 (dppe); X = I, L2 = 2P(OMe)3) or [Mo(OCMe2)L2(η-C7H7)]+ (L2 = dppe, Ph2PCH2PPh2 (dppm)) with the terminal alkynes HCCR; use of [MoBr(dppe)(η-C7H7)] as a precursor is facilitated by an improved, one-step synthesis from [MoBr(CO)2(η-C7H7)]. Syntheses of the 2-oxacyclocarbene complexes [Mo(CCH2CH2(CH2) x O)L2(η-C7H7)]+ (x = 1, L2 = dppm (1), dppe (2); x = 2, L2 = dppm (3), L2 = dppe (4)), the vinylidenes [Mo{CC(H)(CH2)2CH2OH}(dppe)(η-C7H7)][PF6] (5), [Mo{CC(H)(CH2)xPh}(dppe)(η-C7H7)]+ (x = 2 (6), 1 (7)), and [Mo{CC(H)Ph}{P(OMe)3}2(η-C7H7)]+ (8), and the first examples of monometallic molybdenum allenylidene complexes, [Mo(CCCRPh)(dppe)(η-C7H7)]+ (R = Ph (9), Me (10)) are reported. X-ray structural studies on complexes 8 and 9 have determined Mo−Cα distances as follows: 8, 1.929(3) Å; 9, 1.994(3) Å. In 8, the vinylidene ligand substituents lie in the pseudo mirror plane of the MoL2(η-C7H7) auxiliary (vertical orientation) with the phenyl group located syn to the cycloheptatrienyl ring, whereas the allenylidene ligand substituents of 9 are perpendicular to the pseudo mirror plane (horizontal orientation). This series of atypical orientations of cumulenylidene ligand substituents, imposed by the cycloheptatrienyl molybdenum auxiliary, has been investigated further by variable-temperature NMR spectroscopy and quantum-chemical theoretical calculations. A DFT analysis of the complexes [Mo(CCH2)(dppe)(η-C7H7)]+ (11), [Ru(CCH2)(dppe)Cp]+ (12), and [Mo(CCCMePh)(dppe)(η-C7H7)]+ (10) concurs with experimentally determined cumulenylidene ligand orientations. A separate analysis of the fragments [Mo(dppe)(η-C7H7)]+ and [Ru(dppe)Cp]+ reveals that the HOMO of the [Mo(dppe)(η-C7H7)]+ fragment includes a significant contribution from the metal d z 2 orbital, whereas the HOMO of the [Ru(dppe)Cp]+ fragment is based on a metal d xy orbital, orthogonal to the HOMO of the [Mo(dppe)(η-C7H7)]+ unit. In cumulenylidene complexes of the Mo(dppe)(η-C7H7) auxiliary, interactions between the d z 2 -based HOMO of the metal fragment and the vacant LUMO of the cumulenylidene ligand dominate the control of ligand orientation and thus account for the observed structures.

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m-, and p-cresol by aqueous persulphate solutions is strongly catalysed by silver, ferrous, or ferric, but not by other ions examined. Oxidation by S20,2--Fe3+ is much faster than by Fe3+ alone. Reaction is believed to proceed by mechanisms which involve *SO,radicals and, in the case of silver catalysis, transient higher-valency ions, Ag2+ or Ag3+.Resinous polyphenols constitute almost the entire product from phenol and 0-or m-cresol, but with p-cresol the following known crystalline products of oxidative coupling (-30% in all) were isolated : 2 : 2'-dihydroxy-5 : 5'-dimethyldiphenyl, 2 : 2' : 2"-trihydroxy-5 : 5' : 6"-trimethyl-m-terphenyl, and a tetrahydrodimethyloxodibenzofuran. I n the polyphenols the presence of 3-7 phenol units per molecule is indicated, and they contain, on average, about 0-2 atom of additional oxygen per phenol unit, probably introduced via nuclear hydroxylation, since small amounts of surviving mononuclear quinones were detected.WE recently summarised the results obtained by oxidising various kinds of aromatic compounds with aqueous persulphate solutions, particularly in the presence of metal salts as catalysts (Bacon, Bott, Doggart, Grime, and Munro, Chem. and Ind., 1953, 897). The present communication describes the oxidation, by this method, of phenol and of 0-, m-, and p-cresol.We have found that the inclusion of silver ions, in particular, converts an aqueous persulphate solution into a potent and widely applicable oxidant for organic compounds. This catalytic activity of silver with persulphate, discovered by Marshall (Proc. Roy. SOC. and to some organic reactions. The latter include the oxidation of oxalic acid (Kempf,