DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1998, 3543–3548 3543 The interaction of indium(III) iodide species with substituted ortho- and para-quinones Martyn A. Brown, Bruce R. McGarvey and Dennis G. Tuck Department of Chemistry and Biochemistry, University of Windsor, Windsor, Ontario, Canada N9B 3P4 Received 2nd June 1998, Accepted 25th August 1998 The interactions of substituted ortho- and para-quinones with indium(III) halides and the InI4 2 anion have been studied in non-aqueous solution.para-Quinones and InI3 give rise to stable 1 : 1 adducts, which are diamagnetic in the solid state, but which decompose in solution to form (p-sq)InI2 derivatives, where p-sq~2 is the corresponding semiquinonate. With ortho-quinones, the reaction products are (o-sq)InI2 which react with 4-methylpyridine (pic) to form (o-sq)InI2pic2. The electron spin resonance spectra of these products, and their solution chemistry, are discussed. The reactions involve intramolecular one-electron transfer, resulting in oxidation of the iodide ligand.In contrast, the reaction of 3,5-di-tert-butyl-1,2-benzoquinone with InI4 2 apparently involves intermolecular electron transfer; in this case, the products are I3 2 and the corresponding catecholate (dbc), isolated as the solid InI(dbc)pic2. The mechanisms of these various processes are discussed. The oxidation of Main Group elements, and of the lower oxidation state derivatives of such elements, has been the subject of a number of papers from this laboratory.The most significant conclusions include the identification of successive one-electron transfer processes in such redox reactions, and the confirmation of a mechanism involving nucleophilic attack by a quinone at the appropriate metal or non-metal centre. Both electron spin resonance spectroscopy and X-ray crystallography have been important experimental techniques in these investigations, and the use of these and other methods has been discussed elsewhere.1,2 We have recently carried out a series of experiments in which both ortho- and para-quinones interact with the halide of a Main Group metal in its highest oxidation state.In some cases, it has been possible to characterize crystalline adducts of such systems, and in others there is clear evidence of intramolecular electron transfer within the complex. The present paper reports studies of the interaction of a range of ortho- and paraquinones with neutral and anionic halide derivatives of indium(III).With para-quinones, we have isolated 1 : 1 adducts of InI3, which are stable in the solid state, but which decompose in non-aqueous solution, forming paramagnetic species. ortho- Quinones react directly with InI3, to give compounds in which indium(III) is coordinated by two halides and a semiquinonate ligand. These results appear to involve a hitherto unrecognized type of intramolecular electron transfer reaction, with important implications in Main Group chemistry.We have also observed a reaction between an ortho-quinone and the InI4 2 anion, and here the course of the electron transfer is apparently through an intermolecular attack of the quinone on the ligand, a process which is similar to that found in reactions of quinones with organometallic substrates.3 The quinones studied in the present work, and the abbreviations used, are shown right. Experimental Indium halides were prepared by the thermal reaction of the elements in refluxing xylene, and the salt Et4N[InI4] was synthesized from the reaction of Et4NI and InI3 in ethyl acetate (Found: C, 13.2; H, 2.65.Calc. for C8H20InI4: C, 12.8; H, 2.65%). Substituted quinones, and organic bases, were dried over sodium hydroxide and recrystallised under nitrogen. Solvents were distilled from, and stored over, drying agents, and degassed before use. All reactions were carried out in an atmosphere of dry nitrogen, and reaction products were handled by the normal methods for air-sensitive materials.Electron spin resonance (ESR) spectra were recorded on a Bruker ESP-300E instrument operating in the X-band region, using the calibration and other techniques outlined elsewhere.4 O O O O But But O But But O O X4 X = Cl, Br p-dbbq phenanthrenequinone (pq) O – p-dbbsq• – But O o-dbbq O But But O – O – But But O O But o-dbbsq• – dbc2– •– O O O O X4 X = Cl, Br (Cl4q, Br4q) 1,2-naphthoquinone (nq)3544 J.Chem. Soc., Dalton Trans., 1998, 3543–3548 Table 1 Characterization of derivatives of InI3 and ortho-quinones Identifying Analysis (%) a o-Quinone 3,5-di-tert-butylbenzo- Tetrachlorobenzo- Tetrabromobenzo- 1,2-naphtho- Phenanthrene- Compound (sq)InI2 (sq)InI2pic2 (sq)InI2 (sq)InI2pic2 (sq)InI2 (sq)InI2pic2 (sq)InI2 b (sq)InI2pic2 (sq)InI2 c (sq)InI2pic2 number 1 1A 2 2A 3 3A 4 4A 5 5A Yield (%) 75 65 55 45 38 26 53 42 65 58 Colour Purple Brown Red-orange Red Red Orange Dark blue Dark green Green Brown C 28.5 (28.5) 40.0 (40.3) 12.2 (11.7) 27.6 (27.0) 9.50 (9.10) 22.2 (22.1) 22.9 (22.8) 37.2 (37.0) 28.1 (29.1) 41.6 (40.9) H 3.35 (3.40) 4.30 (4.40) 0.14 (0) 1.80 (1.75) 0.02 (0) 1.80 (1.45) 1.35 (1.15) 2.90 (2.80) 1.70 (1.40) 3.00 (2.90) a Calculated values in parentheses.b Mass spectrum; M1 = 527 observed. c Mass spectrum; M1 = 557 observed. Microanalysis was by Canadian Analytical Services. X-Ray crystallographic studies were by the methods previously described.4,5 Mass spectra were recorded on a Shimadzu 14-B instrument operating in the EI mode, with Sun Sparc software.In this paper, we follow the previous practice of identifying the triad of quinone, semiquinone and catecholate by the abbreviations q, sq~2, and cat22, with appropriate prefixes. Preparative studies In a typical experiment with ortho-quinones, a solution of the quinone in tetrahydrofuran (5 mmol in 20 cm3) was added to a stirred solution of InI3 (5 mmol) in the same solvent.In every case, a colour change was observed, with the fastest reaction being with di-tert-butyl-o-benzoquinone. Samples were removed for ESR analysis, and approximately half of the remaining mixture cooled to 0 8C; this led to the precipitation of coloured solids which were shown by analysis to be the corresponding (sq)InI2 derivatives (see Table 1 for analytical results and related experimental data). A six-fold excess of picoline (pic; 4-methylpyridine) was added to the remaining reaction mixture, the volume of the solution reduced by 50%, and the residue cooled to 0 8C; the crystals which formed were identified analytically as the bis(picoline) adducts (sq)InI2pic2.In the case where sq~2 = 3,5- di-tert-butyl-o-benzosemiquinonate (dbbsq) an X-ray crystallographic study showed that this compound was structurally identical with the material formed in the reaction between indium(II) iodide and the corresponding ortho-quinone.5 (Unit cell dimensions, a = 13.0097(5), b = 13.302(4), c = 10.811(5) Å, a = 97.677(4), b = 107.992(3), g = 104.003(4)8, U = 1681.9(6) Å3.Found5 for (dbbsq)InI2(pic)2, a = 13.013(3), b = 13.317(3), c = 10.828(5) Å, a = 97.71(3), b = 107.98(3), g = 103.92(3)8, U = 1684.8(1.2) Å3). We also attempted to prepare adducts with pyridine as the neutral donor, but in each case the analytical results were less than satisfactory, except in the case of phenanthrenequinone (Found: C, 39.4; H, 2.93. Calc.for (psq)InI2py2, C24H18O2N2InI2: C, 39.2; H, 2.47%), and this aspect of the work was not continued. A similar sequence of reactions starting with InCl3 gave the analogous (dbbsq)InCl2pic2 (Found: C, 52.7; H, 6.09. Calc. for C26H24O2N2Cl2In: C, 52.7; H, 5.74%) In each case, the infrared spectra of both the initial products and the picoline adducts showed that n(C]] O) of the o-quinones, in the region 1650–1695 cm21, had disappeared and was replaced by n(C–O) modes at 1440–1490 cm21 (cf.ref. 1). When para-quinones were used in essentially identical experiments, the products were the 1 : 1 adducts, q?InI3, which were isolated and analyzed (Table 2). It was not possible to obtain material of suitable quality for X-ray crystallography from these experiments. Studies with InI4 2 A rapid reaction, identified by a colour change, occurred when millimolar quantities of Et4N[InI4] and dbbq in tetrahydrofuran were mixed together at room temperature.The resultant brown solution was divided into two equal portions. Evaporation of one of these to 50%, followed by cooling, gave a dark brown powder, which was identified analytically as Et4NI3 (Found: C, 18.5; H, 3.82. Calc. for C8H20NI3: C, 18.8; H 3.91%). 13C NMR (Me4Si = 0): d 7.995 CH3, 32.286 CH2. IR n(C–H) 3009–2908, n(C–N) 1585, 1443, 1416 cm21. Yield 100%, based on the initial quantity of cation. Samples of the remaining portion were used for ESR studies (see below).Addition of picoline to this solution gave a colourless precipitate, identified as InI(dbc)(pic)2 (Found: C, 49.5; H, 5.25. Calc. for C26H34N2O2InI: C, 48.2; H, 5.25%). The infrared spectrum confirmed the presence of catecholate, with n(C–O) at 1463, 1433 and 1415 cm21. Similar experiments were attempted using toluene as the reaction medium, but these were unsatisfactory because of the insolubility of the InI4 2 salt, although the general course of the reaction appeared to be similar to that described above.Results and discussion Reactions with ortho-quinones The results in Table 1 for compounds numbered 1–5 show that the reaction of ortho-quinones with InI3 produces (sq)InI2 species, which can be obtained as insoluble solids at 0 8C. The molecularity of these compounds is not known, but treatment with excess picoline yields the bis-adduct, which in the case of (dbbsq)InI2pic2 was shown to be crystallographically identical with the mononuclear six-coordinate compound obtained from the reaction the reaction of dbbq and In2I4.5 The initial overall reaction is dbbq 1 InI3 æÆ (dbbsq)InI2 1 I? (1) followed by 2I? æÆ I2 (2) Table 2 Characterization of adducts of InI3 and para-quinones Yield Analysis (%) a p-Quinone Benzo 2,6-Di-tert-butylbenzo b,c Tetrachlorobenzo Tetrabromobenzo 1,4-Naphtho (%) 80 73 26 35 10 Colour Grey Red Yellow Orange Brown C — (11.9) 23.7 (23.5) 9.70 (10.1) 7.94 (7.83) 15.5 (15.2) H — (0.67) 2.95 (2.80) 0.04 (0) 0.03 (0) 1.08 (0.95) a Calculated values in parentheses.b For 1 : 1 adduct with InCl3, orange, C 38.0 (38.1), H 4.10 (4.53), 62% yield. c Mass spectral peaks include m/z = 496 (InI3).J. Chem. Soc., Dalton Trans., 1998, 3543–3548 3545 and (dbbsq)InI2 1 excess pic æÆ (dbbsq)InI2pic2 (3) Reactions (1) and (2) are complete within about 15 min, with the relative rates, as judged by the colour change, in the order dbbq > Br4q > CI4q > nq > pq, and InI3 > InCl3.We return to the mechanistic details of eqn. (1) below. In each case, the reaction of InI3 and o-quinone gave rise to solutions which were strongly ESR active, as would be expected if the product is a semiquinone derivative. The generation of radical species by the interaction of dbbq with indium and gallium trihalides was reported some years ago, but the reaction pathway was not apparently explored.6,7 In the present studies, the system most thoroughly explored involved InI3 1 dbbq, and Fig. 1a shows the ESR spectrum of the (diluted) solution resulting from this reaction. The addition of excess picoline caused marked changes, giving rise to a spectrum (Fig. 1b) essentially identical to that assigned previously5 to the sixcoordinate indium(III) complex (dbbsq)InI2pic2. The parameters found for Fig. 1b by simulation are g = 2.0038, AIn = 4.9 G, AH = 3.6 G (1 proton) (1 G = 0.1 mT), compared with the earlier values g = 2.00391, AIn = 4.86 G, AH = 3.42 G (1H), 0.36 G (9H): in this spectrum, and those in Fig. 1a, we did not observe any splitting by the proton on C3, as is commonly the case in derivatives of dbbsq.8 Fig. 1a can be analysed as the ESR spectrum of a mixture of two closely related indium(III) species; for one, g = 2.0032, AIn = 8.93 G, AH = 3.65 G (1H), and for the other g = 2.0032, AIn = 8.50 G, AH = 3.65 G (1H). The simulation in Fig. 1a assumes that these two species are present in equimolar proportions, and we therefore suggest that eqn.(1) is followed by 2 (dbbsq)InI2 (dbbsq)IInI2InI(dbbsq) (4) in which the dimerisation is presumed to involve iodide bridging, In–m-I2–In, similar to that reported for In2I6 in nonaqueous solution.9 Such a dimer can exist as cis and trans isomers, which explains the identification of two similar AIn Fig. 1 a, ESR spectrum of the (diluted) solution arising from the reaction of InI3 and o-dbbq, at room temperature.The upper trace is the experimental result, and the lower is the simulated spectrum, using the parameters discussed in the text. b, The same solution, after addition of a six-fold excess of picoline. values. These structures are preferred to the form (dbbsq)2- InI2InI2, which does not give two stereoisomers. The stereochemistry of these various species is an important factor in these arguments. The (dbbsq)InI2 monomer must be highly strained, since it is diYcult for a pseudo-tetrahedral molecule to accommodate the bidentate semiquinonate, given that the bite angle for this ligand is ca. 758 (cf. ref. 5). In a dimeric molecule, indium has pentagonal bipyramidal stereochemistry, and the consequent lowering of strain therefore serves to move eqn. (4) to the right. Both cis and trans dimers can be readily converted to the six-coordinate (dbbsq)InI2pic2 by excess picoline. Coordination by an electron-donating neutral ligand lessens the eVective positive charge at the metal centre, thereby weakening the interaction of the unpaired electron and lowering the hyperfine constant AIn from the relatively high value of ca. 8.6 G in the dimers to one more typical of six-coordinate indium(III) complexes. In an attempt to further characterize these dimeric species, we recorded the ESR spectra of the frozen solution (Fig. 2a), and the associated half-field resonance (Fig. 2b). Surprisingly, the simulation of these spectra identifies the low temperature species as being an S = ��� state, rather than a biradical, and the predominant complex under these conditions is therefore In(dbdsq)3. This molecule, which has been prepared independently 10 by the metathesis of InI3 and 3Na1dbbsq2, is an analogue of Ga(dbbsq)3, whose preparation and crystallographic structure were reported earlier.11 The simulation for S = ��� state assumed a spin-Hamiltonian of the form H = gBeS·H 1 AIn S· I 1 D[3 S2z 2 1 3 – S (S 1 1)] (5) with the parameters g = 2.003, AIn = 8 ± 0.5 G, and D = 103 ± 5 Fig. 2 a, ESR spectrum of frozen solution at 100 K from Fig. 1a. b, The half-field transition. In I In I O O O I O I In I In I O O O I I O • • • • cis trans3546 J. Chem. Soc., Dalton Trans., 1998, 3543–3548 G. The corresponding values for the gallium complex are g = 2.003, D = 108; the slightly lower value of D for the indium species is in keeping with the larger ionic radius of the latter element. In addition to the dimerisation processes discussed above, the solution chemistry of the (dbbsq)InI2 product of eqn.(1) must therefore also involve the equilibria InX3 InX2Y InXY2 InY3 (6) where X = I, Y = dbbsq. Such facile redistribution reactions are a known feature of the chemistry of indium(III) complexes in non-aqueous solution,9 and in the present context explain the presence of di- and tri-radical species. The relative quantity of each species will be a function of solvent, temperature, and the nature of the semiquinonate anion, and it is therefore understandable that the predominant trimer seen at 100K is not observed at room temperature.The ESR spectra of solutions produced by the reaction of o-Cl4q and o-Br4q with InI3 were weak, due to the poor solubility of the (X4sq)InI2 products, and of their picoline derivatives (2–3A, Table 1). There are also some diVerences in the case of the derivatives of 1,2-naphthoquinone; the AIn value in the presence of excess picoline is 3.6 G, in reasonable agreement with that for the dbbsq analogue, but the spectrum of the initial reaction solution shows no indium hyperfine coupling, suggesting that the species in solution are the free napththosemiquinonatInI3.In the case of phenanthrenequinone, the reaction solution gave g = 2.0028, AIn = 1–2 G, but the simulation of the picoline adduct spectrum was clearer, with AIn = 2.6 G, AH = 2.25 (1H) and 1.35 G (1H), and g = 2.0036. These results in general are in keeping with those for dbbq 1 InI3, although the naphthoquinone results emphasize the significance of the solution equilibria, and their dependence on the properties of the o-quinone involved.The main feature of these reactions is the oxidation of a ligand bonded to a metal which is in its highest oxidation state. In previous studies 5,8,12 of the reactions of substituted orthoquinones with indium-(I) and-(II) halides, we established that oxidation occurred at the metal centre, leading to the eventual production of sq~2 or cat22 derivatives of indium(III), depending on the detailed behaviour of the system.The present results show that a diVerent reaction q 1 InX3 æÆ (sq?)InX2 1 X? (7) can also occur, and we note that this parallels a known fast solution-phase reaction in the case of iodide 13 q 1 I2 æÆ sq~2 1 ��� I2 (8) While this readily explains the reactions of InI3, the reaction dbbq 1 InCl3 æÆ (dbbsq?)InCl2 1 Cl? (9) is more surprising, since Cl2 is not oxidized by ortho-quinones in aqueous solution, but it must be emphasized in this context that we are dealing here with a complex of a metal in its highest oxidation state, and that the redox behaviour of a bonded halide ligand in such a molecule will be quantitatively diVerent from that of the free anion in aqueous solution. The first step in the reaction is the coordination of the quinone to the metal centre, as is suggested by the chemistry of the para-quinone systems (see below), and confirmed by studies of complex formation between ortho-quinones and AlCl3 or SnX4 (X = Cl, Br),14 and this must be followed by intramolecular electron transfer within the bonded system.q In X e One important diVerence between this process and the solution phase reaction of eqn. (7) lies in the entropy of activation. In a series of reactions involving tetrahalogeno-p-quinones and MI (M = Na1, K) in acetone,13 DS‡ was found to be in the order of 280 J K21 mol21, but this parameter is probably close to zero for an intramolecular electron transfer in a relatively large molecule in non-aqueous solution, and to this extent, the energetics of the latter process are more favorable than for the solution reaction.The detailed implication of these principles will be the subject of future work. Reactions with para-quinones The analytical results in Table 2 show that the products of the reaction between indium(III) iodide and a series of substituted para-quinones are the 1 : 1 adducts, which are stable at room temperature in the absence of moisture.An analogous compound was also obtained with indium(III) chloride. This adduct formation is not surprising, given the known properties of the indium(III) halides,9 and it seems reasonable to assume that these are four-coordinate monomeric species in the solid state. As noted above, crystallographic investigations were not possible, but we have recorded the infrared spectra with particular reference to the carbonyl stretching mode, which is typically in the region of 1650–1690 cm21 for the parent quinones, and is sometimes observed as a doublet due to Fermi resonance.15,16 For p-dbbq, the complex has a vibration at 1655 (cf.n(C]] O) at 1655 cm21 in the parent p-quinone), and similar features are seen in the adducts of p-Br4q, p-Cl4q and 1,4-naphthoquinone. We discuss the p-C6H4O2 system below. These spectra are compatible with weak bonding of p-q to InI3.Similar results have been obtained with adducts of InI3 and cyclic ketones, for which both X-ray and infared results show only small changes in the properties of the C]] O group on coordination.14 The solid complexes show no significant ESR activity, in keeping with the above structure which implies no singleelectron transfer, but significant spectra are observed on dissolution in non-aqueous solvents. The solution spectra were recorded under a variety of conditions, and q : InI3 ratios, and all show clear evidence of a free radical coupled to indium. Most of the spectra are apparently of a mixture of species, but that shown in Fig. 3 analyses as being from an essentially single species and the spectrum was well simulated with the parameters g = 2.0065, AIn = 1.88 G, AH = 3.45 G (4H). The identifi- cation of four equivalent hydrogen nuclei requires the molecule in question to contain two p-dbbsq~2 groups, and two possible structures are shown below.The simulation results eliminate structures analogous to those proposed for the ortho-quinone system, since these would require contributions from two indium and four hydrogen atoms. Although we observed a half-field transition in the frozen solution of Fig. 3, it was not possible to deduce the D value, which might have cast light on this matter. We conclude that the solution chemistry of this 1 : 1 adduct involves as the first step an intramolecular electron transfer which is facilitated by the elimination of a halogen atom. This latter process may require solvation O O In I I I I I In I I In solv I In p-sq p-sq p-sq p-sqJ.Chem. Soc., Dalton Trans., 1998, 3543–3548 3547 (p-q)InI3 æÆ (p-sq?)InI2 1 I?(solv) (10) 2 I?(solv) æÆ I2 (11) and/or I?(solv) æÆ decomposition products (12) Eqn. (10)–(12) are obviously reactions whose rates will depend on solvent, the quinone, and temperature. The semiquinonate derivative (p-sq?)InI2 may be the starting point for redistribution processes, following eqn.(6). Dimerisation is also possible, but the presumably low steady state concentrations of (p-sq?)- InI2 argue against this, in contrast to the ortho-quinone system in which (o-sq?)InI2 is initially the predominant solute species. A reaction which is more probable than dimerisation is association with unreacted (p-q)InI3 to give (p-sq)InI–m-I–InI2(p-q), which can then be the starting point for redistribution processes.Given these possibilities, it is not surprising that the ESR spectra demonstrate the presence of a mixture of radicalcontaining complexes. The most important conclusion is that the para-quinone adducts studied are stable four-coordinate diamagnetic monomers in the solid state, decomposing in non-aqueous solution to give semiquinonate derivatives. The conclusion that intramolecular electron transfer is aVected by the phase seems counter-intuitive, but the critical factor here is the removal of halogen by eqn.(10). The diVerent solution behavior of the ortho- and para-quinone systems reflects both the redox properties of the quinones, and their diVerent coordinating properties. In particular the larger hyperfine constants for indium in the o-quinone complexes (5–8 G), compared to the p-quinones (ª2 G) shows that bidentate coordination produces a stronger interaction between ligand and metal centre. The relative strengths of the ESR signals for the para-quinone systems suggests that eqn.(10) goes to the right in the order p-dbbq > p-Cl4q > p-Br4q ª p-nq, with only very weak activity being observed in the last two systems. The absence of biradical activity in all these systems may be evidence of the stability of (p-sq)InI2 species relative to the redistribution processes. The p-C6H4O2 system diVers substantially from the others just discussed. The solid is strongly ESR-active, and the solution spectrum shows strong coupling to indium(III), but no evidence was obtained for biradical species.The infrared spectrum had no features in the n(C]] O) region. The solid slowly turns grey on standing, and we conclude that the adduct InI3(p-C6H4O2) is sensitive to both air and moisture, and that the strong ESR activity is evidence of decomposition rather than of intramolecular electron transfer, but we did not investigate these eVects in any detail. Fig. 3 ESR spectrum of a dilute solution of p-dbbq 1 InI3 (mole ratio 1 : 2) in tetrahydrofuran at room temperature.Upper trace, experimental result: lowce, simulated spectrum, using the parameters discussed in the text. Reaction with InI4 2 The previous systems, involving InI3 with o- or p-quinones, have been discussed in terms of coordination followed by intramolecular electron transfer. In the course of this work, we also found an unexpected reaction between dbbq and the InI4 2 anion.An important experimental point is that this reaction can only be studied spectroscopically by using salts of Et4N1 or some similar cation which resists oxidation by the o-quinone; initial studies with tetraphenylphosphonium salts were hindered by a reaction apparently involving this cation. The production of Et4NI3 in quantitative yield, and of (dbc)InIpic2 in the presence of picoline, shows that the overall reactions are Et4NInI4 1 dbbq æÆ Et4NI3 1 (dbc)InI (13) (dbc)InI 1 excess pic æÆ (dbc)InIpic2 (14) Eqn.(13) begs the question of mechanism, and we propose a process based on the work of Davies et al.17 for reactions such as q 1 Ph4Sn æÆ sq?(Ph?)SnPh3 æÆ (sq?)SnPh3 1 Ph? (15) which was substantiated for a range of substituted quinones. The same mechanism has been invoked for the reaction between o-quinones and Sn2Ph6,3 and for the oxidation of phenyl, as in LiPh, by o- and p-quinones to give Li1(sq~2).18,19 Equally important are that Ph4Sn has no acceptor properties,20 which eliminates the possibility of nucleophilic attack at the metal centre, and that the solution chemistry of (dbbsq)SnPh3 shows the importance of redistribution reactions subsequent to eqn.(15).3 The detailed discussion of eqn. (13) and (14) also begins with the lack of evidence 9 for any acceptor properties for InI4 2, in contrast to InCI4 2 and InBr4 2, so that the primary process is assumed to be analogous to eqn. (15) dbbq 1 InI4 2 æÆ [(dbbsq?)(I?)InI3]2 æÆ dbbsq~2 1 InI? 4 (16) followed by InI4 ? æÆ InI31I? (17) dbbsq~2 1 InI3 (dbbsq?)InI2 1 I2 (18) (dbbsq?)InI2 æÆ (dbc)InI 1 I? (19) 2I? 1 I2 æÆ I3 2 (20) This sequence explains the products identified (see Experimental section), and is compatible with the ESR spectra of the reaction solution.The results for the dbbq/InI4 2 reaction raise an ambiguity in the matter of the initial step in the reaction of o-quinones with InI3. As noted above, p-quinones form stable 1 : 1 adducts with InI3, implying that nucleophilic attack is probable in the o-quinone/InI3 system. Earlier evidence from NMR studies of InI3dppe mixtures 21 (dppe = 1,2-bis(diphenylphosphino)- ethane) show that the formation of the 1 : 1 complex dppe 1 InI3 æÆ InI3(dppe) (21) lies strongly to the right, which supports the coordinative mechanism of eqn.(1). On the other hand, InI3 in toluene is present as the dimer In2I6, in which indium is psuedotetrahedrally coordinated, as it is in InI4 2, so that a reaction sequence analogous to that in eqn.(14)–(16) can also be3548 J. Chem. Soc., Dalton Trans., 1998, 3543–3548 constructed. The presence of the dimer is not itself an argument against the coordinative mechanism, as has been shown for the ddpe case,21 and we therefore favour the model proposed, earlier. Further work on this is planned. Acknowledgements This work was supported in part by Research Grants (to B. R. M. and D. G. T.) from the Natural Sciences and Engineering Research Council of Canada.References 1 D. G. Tuck, Coord. Chem. Rev., 1993, 112, 215. 2 B. R. McGarvey, A. Ozarowski and D. G. Tuck, Inorg. Chem., 1993, 32, 4474. 3 M. A. Brown, B. R. McGarvey, A. Ozarowski and D. G. Tuck, J. Organomet. Chem., 1998, 550, 165. 4 T. A. Annan, M. A. Brown, A. A. El-Hadad, B. R. McGarvey, A. Ozarowski and D. G. Tuck, Inorg. Chim. Acta, 1994, 225, 207. 5 M. A. Brown, B. R. McGarvey, A. Ozarowski and D. G. Tuck, Inorg. Chem., 1996, 35, 1560. 6 G. A. Razuvaev, G. A. Abakumov and E. S. Klimov, Dokl. Akad. Nauk SSSR, 1971, 201, 624. 7 G. A. Abakumor and E. S. Klimov, Dokl. Akad. Nauk SSSR, 1972, 202, 827. 8 T. A. Annan, R. K. Chadha, P. Doan, D. H. McConville, B. R. McGarvey, A. Ozarowski and D. G. Tuck, Inorg. Chem., 1990, 29, 3936. 9 D. G. Tuck, Comprehensive Coordination Chemistry, eds. G. Wilkinson, R. D. Gillard and J. A. McCleverty, Pergamon Press, Oxford, 1987, vol. 3, ch. 25.2, p. 165. 10 A. A. El-Hadad, M.Sc. Thesis, University of Windsor, 1996. 11 A. Ozarowski, B. R. McGarvey, A. A. El-Hadad, Z. Tian, D. G. Tuck, D. J. Krovich and G. C. DeFotis, Inorg. Chem., 1993, 32, 841. 12 T. A. Annan and D. G. Tuck, Can. J. Chem., 1988, 66, 2935. 13 M. Sasaki, Rev. Phys. Chem. Jpn., 1996, 39, 27. 14 T. L. Brown, Spectrochim Acta, 1963, 19,1065. 15 T. Anno and A. Sado, Bull. Chem. Soc. Jpn., 1958, 31, 734. 16 M. A. Brown and D. G. Tuck, unpublished work. 17 A. G. Davies and J. A. A. Hawairi, J. Organomet. Chem., 1983, 251, 53. 18 M. A. Brown, B. R. McGarvey, H. Ozarowski and D. G. Tuck, J. Am. Chem. Soc., 1996, 118, 9691. 19 M. A. Brown, B. R. McGarvey and D. G. Tuck, J. Chem. Soc., Dalton Trans., 1998, 1371. 20 A. G. Davies and P. J. Smith, Comprehensive Organometallic Chemistry, eds. G. Wilkinson, F. G. A. Stone and E. W. Abel, Pergamon Press, Oxford, 1982, vol. 2, ch. 11, p. 548. 21 M. A. Brown, D. G. Tuck and E. J. Wells, Can. J. Chem. 1996, 74, 1535. Paper 8/04124E