David O'n. Smith

13C-{103Rh} double resonance spectra of rhodium(I) and rhodium(-I) carbonyl complexes

Abstract 103 Rh Chemical shifts of a variety of mono- and di-nuclear rhodium carbonyl complexes are reported together with the modifications to the probe and decoupler unit of a JEOL PS-100 PFT spectrometer which enable these 103 Rh-decoupled 13 C NMR measurements to be made. These data are discussed in conjunction with 13 C NMR data on other rhodium carbonyls.

Bimetallic iron–rhodium anionic carbonyl clusters: [Fe2Rh(CO)x]–(x= 10 or 11), [FeRh4(CO)15]2–, [Fe2Rh4(CO)16]2–, and [FeRh5(CO)16]–

The synthesis and chemical behaviour of the new iron-rhodium anionic carbonyl clusters [Fe2Rh(CO)x]–(x= 10 or 11), [FeRh4(CO)15]2–, [Fe2Rh4(CO)16]2–, and [FeRh5(CO)16]– are reported. Low-temperature multinuclear n.m.r. studies (13C,13C-{103Rh}, and 103Rh) on the penta- and hexa-nuclear clusters allow their structures in solution to be unambiguously established and their fluxional behaviour has been investigated through variable-temperature measurements. None shows rearrangement of the metal polyhedron.

Contributions to organoboron chemistry : XV. Aminodiphenylboranes

Abstract The synthesis of a series of aminodiphenylboranes is reported together with the results of a detailed study of their 13 C NMR spectra. All compounds exhibited peaks assignable to the carbon atom directly bonded to boron when run under appropriate conditions. The 13 C spectra of primary aminodiphenylboranes provided further evidence for restricted rotation about the B—N bond.

13C{103Rh} nuclear magnetic resonance of [Rh7(CO)16]3−

Abstract Specific 103 Rh spin-decoupling has been used to make a complete assignment of the 13 C NMR spectrum of [Rh 7 (CO) 16 ] 13− . At room temperature 3 μ 2 -carbonyls exchange with 3 μ 1 -carbonyls; it is shown that this carbonyl exchange occurs around the outside of the metal polyhedron rather than rotation of part of the metal skeleton within the carbonyl polyhedron. The rhodium chemical shifts show a large alternation from low to high field along the C 3 -axis of the cluster.

Phenylboranes.direct observation of p13C nuclear resonances of carbon atoms bonded directly to boron

Abstract Neat samples of a wide variety of phenylboranes at room temperature exhib- it well resolved resonances for carbon atoms bonded directly to boron, in con- trast to their solutions where such resonances are either extremely broad or en- tirely undetectable.

Heteronuclear transition metal–alkyne clusters. Part 1. Reactions of tris(alkyne)monocarbonyltungsten complexes with octacarbonyldicobalt. Synthesis, X-ray crystal structure, and two-dimensional nuclear magnetic resonance studies of [WCo2(µ-C2Et2)(µ-C4Et4)(CO)8]

Reactions between the compounds [W(C2R2)3(CO)](R = Et or Pr) and [Co2(CO)8] afford the trinuclear metal complexes [WCo2(µ-C2R2)(µ-C4R4)(CO)8]. The molecular structure of [WCo2-(µ-C2Et2)(µ-C4Et4)(CO)8] has been established by an X-ray diffraction study. The structure has a non-linear open chain of metal atoms [Co–W–Co 153.6(1)°] in which one tungsten–cobalt bond [2.732(1)A] is bridged by a 3-hexyne ligand in a perpendicular co-ordination mode, while the second tungsten–cobalt bond [2.673(1)A] is bridged by an alkyne-derived butadiene ligand, π-bound to tungsten and σ-bound to cobalt. The cobalt atoms are also ligated by three terminal carbonyl groups and the tungsten by two such groups. A full assignment of the 1H and 13C-{1H} spectra of [WCo2(µ-C4Et4)(µ-C4Et4)(CO)8] using two-dimensional [1H-1H] and [13C-1H]-COSY n.m.r. spectroscopy reveals that alkyne rotation does not occur on the n.m.r. time-scale, although fluxional processes produce a mirror plane through the three metals. The complex [WCo2(µ-C2Et2)-(µ-C4Et4)(CO)8] reacts with P(OMe)3 to afford [WCo2(µ-C2Et2)(µ-C4Et4)(CO)7{P(OMe)3}] in which carbonyl substitution at a cobalt centre has occurred.

Restricted rotation about the boronnitrogen bond in aminoboranes

The application of variable temperature 13C NMR to the study of a series of chlorodialkylaminophenylboranes has enabled △G★ values for the rotational barrier, about the boronnitrogen bond, to be determined.

Bimetallic iron–rhodium anionic carbonyl clusters [Fe2Rh(CO)x]–(x= 10 or 11), [FeRh4(CO)15]2–, [Fe2Rh4(CO)16]2–, and [FeRh5(CO)16]–

The syntheses and interconversions of mixed iron–rhodium carbonyl clusters are described; a combination of X-ray analysis and multinuclear n.m.r. measurements allowed the structural characterisation of [FeRh4(CO)15]2–, [FeRh5(CO)16]–, and [Fe2Rh4(CO)16]2–, which can all be obtained from the unstable cluster, [Fe2Rh(CO)x]–(x= 10 or 11).

Restricted rotation about the boronnitrogen bond in dialkylaminofluorophenylboranes

Abstract The application of variable temperature 13C NMR to the study of dialkylaminofluorophenylborane has enabled Δ G* values for the rotational barrier about the boronnitrogen bond to be determined.

Synthesis of piloquinone, a metabolite of Streptomyces pilosus ettlinger

Synthesis of piloquinone [1,8-dihydroxy-2-methyl-3-(4-methylpentanoyl)-9,10-phenanthraquinone](1) is described. Of the methods investigated the most successful started from 2,6-dinitrotoluene (48) which was converted into 2-bromo-6-hydroxytoluene (52). This on bromination at –70 to 20° in the presence of isopropylamine gave 3,6-dibromo-2-hydroxytoluene (53) and thence 3,6-dibromo-2-methoxytoluene (54). This was converted by an organometallic method into 4-bromo-2-methoxy-3-methylbenzaldehyde (57) which on Wittig reaction with 2-methoxybenzyltriphenylphosphonium chloride gave 4-bromo-2,2′-dimethoxy-3-methylstilbene (37). The latter was converted, via 4-cyano-2,2′-dimethoxy-3-methylstibene (36), into methyl 2,2′-dimethoxy-3-methylstilbene-4-carboxylate (39), which on u.v. irradiation gave chiefly methyl 1,8-dimethoxy-2-methyl-phenanthrene-3-carboxylate (42). The latter on reduction and oxidation gave 1,8-dimethoxy-2-methylphenanthrene-3-carbaldehyde (44) which on reaction with isopentylmagnesium bromide followed by oxidation with Jones reagent gave 1,8-dimethoxy-2-methyl-3-(4-methylpentanoyl)phenanthrene (63). This on demethylation and acetylation gave 1,8-diacetoxy-2-methyl-3-(4-methylpentanoyl)phenanthrene (64) which on oxidation followed by treatment with base gave piloquinone (1).