Stephen M. Godfrey

The reactions of sulfur and selenium donor molecules with dihalogens and interhalogens

Abstract The structural diversity of 1:1 addition products between sulfur and selenium donor molecules and dihalogens and interhalogens has become of particular interest during the last 10 years, with a wealth of structural publications debating the factors that determine the precise structural motif of a given system. In this article, we review the main crystallographic reports, discuss the structural factors affecting these systems and describe some potential applications for the future.

The structure of triphenylphosphorus–diiodine, Ph3PI2, the first crystallographically characterised dihalogen derivative of a tertiary phosphine

Triphenylphosphine reacts with diiodine in dry diethyl ether to produce Ph3PI2, shown by X-ray crystallography to be a molecular four-coordinate compound Ph3P–I–I, and not the five-coordinate Ph3PI2 or the ionic [Ph3PI]+I–, previously thought to be the only possible solid-state structures for such a compound.

The structure of triphenylphosphorus–dibromine, the first crystallographically characterised bromophosphorane, a compound which has the novel four-coordinate molecular Ph3P–Br–Br geometry

Triphenylphosphorus–dibromine is shown by X-ray crystallography to have a four-coordinate Ph3P–Br–Br ‘spoke’ structure and is isostructural with Ph3P–I–I and Ph3As–I–I; thus forcing us to question the conventional belief that tertiary-organo group 15 adducts with dihalogens have either pentacoordinate R3EX2 or ionic [R3EX]+X– structures in the solid state.

An X-ray crystallorgraphic study of the reagent Ph3PCl2; not charge-transfer, R3P–Cl–Cl, trigonal bipyramidal or [R3PCl]Cl but an unusual dinuclear ionic species, [Ph3PCl+⋯Cl–⋯+CIPPH3]Cl containing long Cl–Cl contacts

An X-ray crystallographic study of the reagent Ph3PCl2 reveals it to be [Ph3PCl+⋯Cl–⋯+ClPPh3]Cl and not trigonal bipyramidal, molecular charge-transfer Ph3P–Cl–Cl or the simple ionic species [Ph3PCl]Cl; this contrasts with the conclusions from all previous spectroscopic data recorded on compounds of stoichiometry R3PCl2 by earlier workers, and represents the first compound of this formula to be crystallographically characterised.

The reaction of gallium metal with (p-MeOC6H4)3AsI2 and Et3AsI2; isolation of a novel gallium(II) arsine complex with a gallium–gallium bond and the X-ray crystal structures of GaI3[(p-MeOC6H4)3As] and Ga2I4(AsEt3)2

The reaction of (p-MeOC6H4)3AsI2 and Et3AsI2 with gallium metal powder produce the metal complexes Gal3[(p-MeOC6H)4As] and Ga2I4(AsEt3)2, respectively; the latter respresents a unique example of a gallium–tertiary arsine complex containing a gallium–gallium bond, and both structures illustrates the subtle effect of the organic substituent on the arsenic atoms.

The isolation from diethyl ether of ionic [(Me2N)3PI]I and [(CH2CHCH2)2PhPI]I, and the crystallographically characterised molecular ‘spoke’ structure PhMe2PI2

Ten new compounds of stoichiometry R3PI2[R3=(o-MeOC6H4)3, (o-MeOC6H4)2Ph, (o-MeOC6H4)Ph2, (p-FC6H4)2Ph, (p-FC6H4)Ph2, (p-CH2CHC6H4)Ph2, (CH2CHCH2)2Ph, (C6H11)Ph2, (PhCH2CH2)3 or (Me2N)3] have been prepared by the direct reaction of PR3 and I2 in diethyl ether solution. The compounds have been characterised by Raman and solid-state 31P-{H} magic angle spinning (MAS) and solution NMR spectroscopy. Solid-state 31P-{H} MAS NMR studies indicate that the predominant solid-state species is the molecular ‘spoke’ structure R3P–I–I; however, in some cases a minor peak was also assignable to the ionic species, [R3PI]I. Additionally, solid-state 31P-{H} MAS NMR studies of (Me2N)3PI2 and (CH2CHCH2)2PhPI2 indicate that, in contrast to all other compounds of stoichiometry R3PI2 prepared in diethyl ether, they are exclusively ionic, [R3PI]I. The crystal structure of PhMe2PI2 shows it to have the molecular ‘spoke’ geometry, PhMe2P–I–I, d(I–I)= 3.408 A, previously observed for Ph3PI2, in agreement with solid-state 31P-{H} MAS NMR results.

Reactions of dihalogenotriorgano-phosphorus, -arsenic and -antimony compounds with [Fe2(CO)9]. Single-crystal structures of the iron(III) complexes [(Ph3PO)2H][FeBr4] and [Ph4Sb][Fel4]·Ph3Sbl2 and of [Fe(CO)3(Ph3P)2]

The reaction of [Fe2(CO)9] with compounds of stoichiometry R3EX2[R3E = Ph3P, (p-MeOC6H4)3P, Me2PhP, Me3As or Ph3Sb, X = I; R3E = Ph3P, Ph3As or Me3As, X = Br] has been investigated and shown to yield diverse products. A series of complexes with the ionic structure [R3EX][Fe(R3E)X3][E = P, R3= Ph3, Me2Ph or (p-MeOC6H4)3, X = I; R3E = Me3As; X = I or Br] has been obtained. The reaction of [Fe2(CO)9] with Ph3PBr2 and Ph3AsBr2, however, resulted in the formation of the iron(III) complexes [(Ph3E)2Br][FeBr4]. Hydrolysis of [(Ph3P)2Br][FeBr4] by trace quantities of water produces [(Ph3PO)2H][FeBr4], the crystal structure of which has been determined. Triphenylantimony diiodide reacted with [Fe2(CO)9] yielding the surprising ionic adduct [Ph4Sb][FeI4]·Ph3SbI2, remarkable not only for the phenyl migration at the antimony atom, but also for the formation of the rare [FeI4]– anion from a zerovalent iron carbonyl complex. The reaction of [Fe2(CO)9] with the milder diphosphine tetraiodide, I2Ph2PCH2CH2PPh2I2, produced [Fe(CO)3(Ph2PCH2CH2PPh2)I][I3], a complex in which three CO ligands are retained.

The reaction of coarse-grain metal powders with phosphoranes: a facile activation of metallic reagents and a novel route to metal–phosphine complexes. The X-ray crystal structures of Mnl2(PPhMe2) and FeBr3(PPhMe2)2

A route to new and existing transition metal phosphine complexes is provided by the reaction of coarse-grain metal powders and phosphoranes in diethyl ether, as exemplified here by Nil3(PMe3)2, FeBr3(PPhMe2)2 and Mnl2(PPhMe2).

The reaction of triorganophosphorus diiodides, R3PI2, with zinc metal powder; dependency of product on R; the X-ray crystal structures of dimeric {ZnI2[P(NMe2)3]}2 and monomeric ZnI2(PPh2Me)2

Abstract Seventeen zinc(II) tertiary phosphine complexes have been synthesised directly from elemental zinc by reaction with the reagents R 3 PI 2 . The complexes have been characterised by elemental analysis and 31 P{H} NMR spectroscopy. The present work represents the first comprehensive study of a wide variety of zinc(II) tertiary phosphine complexes containing different parent tertiary phosphines and the majority of the complexes are reported for the first time. In most cases, reaction of R 3 PI 2 with zinc metal powder in diethyl ether in a 1:1 stoichiometric ratio, produces the dimeric complexes [ZnI 2 (PR 3 )] 2 , analogous to the previously reported [ZnI 2 (PEt 3 )] 2 . In contrast, reaction of R 3 PI 2 (R=Ph 3 , Ph 2 Et, Ph 2 Me) with zinc metal powder produces the monomeric bis complexes ZnI 2 (PR 3 ) 2 and an equimolar quantity of zinc(II) iodide, the latter product being identified by X-ray powder diffraction. The X-ray crystal structures of dimeric {ZnI 2 [P(NMe 2 ) 3 ]} 2 and monomeric ZnI 2 (PPh 2 Me) 2 are also described. The formation of the bis complexes ZnI 2 (PR 3 ) 2 (R 3 =Ph 3 , Ph 2 Me, Ph 2 Et) is surprising and cannot be due to steric factors since complexes containing less bulky tertiary phosphines are shown to be dimeric and the adoption of a monomeric zinc(II) centre increases steric crowding at the metal atom. The existence of the bis complexes is therefore reasoned to be due to favourable Π–Π interactions on the ligands and crystal packing forces.

Structural relationships between o-, m- and p-tolyl substituted R3EI2 (E = As, P) and [(R3E)AuX] (E = As, P; X = Cl, Br, I)

The compounds R3EI2 (R = o-tolyl, E = As, 1a; R = m-tolyl, E = P 1c; R = p-tolyl, E = As, 1d, P, 1e), which display the charge transfer spoke structure, and [(o-tolyl3As)AuCl] 2 have been synthesised and their solid state structures compared to the related complexes [(R3P)AuX] (R = o-tolyl, X = Cl, I, Ia; Br, II; I, III; R = m-tolyl, X = Cl, IV; R = p-tolyl, X = Cl, V, Va; Br, VI; I, VII) on the basis of a similarity of their molecular shape and volume. All of the new compounds 1a, 1c–1e and 2 have been fully spectroscopically characterised and by single crystal X-ray crystallography. The sterically demanding exo3o-tolyl ring conformation is observed for 1a, which is comparable to that reported for o-tolyl3PI21b, with a long As–I bond 2.7351(14) A and short I⋯I distance 2.9528(11) A. The exo3o-tolyl ring conformation is maintained on complexation to gold(I) in 2, but has no significant impact on the expected bond lengths, with As–Au 2.3443(15) A and Au–Cl 2.284(4) A. The exo3 conformation appears to be stabilised in both cases by the formation of a six-fold edge-to-face (EF)6 embrace. It is found that in some cases the structures of the dihalogen adducts and the gold(I) complexes are isomorphous indicating that ligand packing requirements are most significant i.e. for 1c and IV. Where the structures digress this is due either to the greater ability of the dihalogen adduct to engage in hydrogen bonding 1a, b and I–III; or subtle changes in the nature of the tolyl ring embraces 1d, e and V–VII. Subtle changes in the nature of the tolyl ring embraces also account for the different polymorphs I and Ia and V and Va. There is no credible evidence to suggest that the aurophilic contact, seen in only one polymorph Va, exerts any influence on the overall crystal packing. The structural comparisons presented here add further to the applicability of the recently recognised structural mimicking ability of the R3PX2 systems and [R3PAuX] complexes, and that the aurophilic contact is a poor supramolecular synthon.