7408
J . Am. Chem. SOC.1987, 109, 7408-7416
Keggin structure. The previous studies involved V5+ substitution when the central heteroatom was Si, P, or B8 and Pb2+ and Ti4+ substitution when the central atom was P.25939 The Pb2+ complex was atypical,40 involving a temperature-dependent shift of the signal from W(4) far downfield from its position in the other complexes, owing presumably to some rapid exchange, possibly with the lacunary species, and to unusual steric placement of the P b atom.25 All the other complexes, including the present ones, show some remarkably similar, although not identical, features (39) Knoth, W. H.; Domaille, P. J.; Roe, D. C. Inorg. Chem. 1983,22, 198. (40) Tourn6, G. F.; Tourn6, C. M.; Schouten, A. Acta Crystallogr., Sect. B: Struct. Crystallogr. Cryst. Chem. 1982, B38, 1414.
with respect to orders of chemical shifts. In all of the spectra, the most downfield line (most deshielded W's) is for W(1) (the pair of W's sharing edges with the substituted metal), while the most shielded or second most shielded W's are W(4), those sharing corners with the substituted metal. The order of line assignments for the present study of the Zn2+ complexes is most similar to that for the V5+ derivative of 1 1-tungstosilicate.
Acknowledgment. This research was aided by N S F Grant CHE-8406088, by Grant CCB-8504039 from the US.-Spain Joint Committee for Scientific Cooperation, and by an instrument grant from the W. M. Keck Foundation. Parts of the work on substituted a2 Wells-Dawson derivatives were supported a t the University of Oregon by NSF Grant CHE-8612924.
Complexes of (Arylimido)vanadium( V). Synthetic, Structural, Spectroscopic, and Theoretical Studies of V( Ntol)C13 and Derivatives David D. Devore,? Joseph D. Lichtenhan,?Fusao Takusagawa,t and Eric A. Maatta*? Contribution from the Department of Chemistry, Kansas State University, Manhattan, Kansas 66506, and Department of Chemistry, University of Kansas, Lawrence, Kansas 66045. Received March 23, 1987
Abstract: The reactions of VOC13 with various para-substituted aryl isocyanates, p-XC6H4NC0 (X = CH3, CF3, OCH3, F, CI, Br), afford the corresponding (arylimido)vanadium(V) trichloride species, V(NC&4X)C13. The p-tolylimido complex, V(Ntol)CI3, 1, displays an extensive derivative chemistry. The reaction of 1 with Lewis bases affords monoaddition products such as V(Ntol)C13(THF) and V(Ntol)CI3(PPh3). The chloride ligands of 1 readily participate in nucleophilic substitution reactions, affording a range of alkoxide (V(Ntol)Cl,_,(O-t-Bu),: n = 1, 2; n = 2, 3; n = 3, 4), aryloxide (V(Ntol)CI3_,(OAr),: n = 1, 5; n = 2, 6; n = 3, 7; Ar = 2,6-C6H3(CH3)2),and organometallic (V(Ntol)Cl3..,(CH2SiMe3),: n = 1, 8; n = 2 , 9; n = 3, 10; ($-C5H,)V(Ntol)CI2, 11) derivatives. The electronic spectra of complexes 1-10 each display an absorption in the near-IR region at ca. 1000 nm. Complexes 1-7 also display a second absorption in the visible region of the spectrum, and the energy of this absorption increases with increasing electronegativity of the basal ligand donor atoms. The 51VNMR spectra of these (arylimido)vanadium(V) complexes have been determined; 5'V chemical shifts in this series span a range of 1700 ppm. The 5'V chemical shifts also correlate with the electronegativity of the basal ligand donor atoms. The lowest field position is observed for 10 (S(51V)= +1048), and a regular progression of S(51V)to higher field occurs as the purely o-donating alkyl groups are replaced by ligands of increased electronegativity and increased r-donating ability. The observed correlations of the electronic and 51VN M R spectra with the chemical constitutions of complexes 1-10 are explained in terms of a dominating paramagnetic shielding contribution. Extended Hiickel calculations on several model complexes are used to provide an explanation of the electronic factors underlying the disparate 51Vchemical shifts observed for complexes 1-10 and related vanadium(V) complexes bearing oxo and alkylimido ligands. An X-ray crystal structure determination reveals that complex 6 possesses a dimeric structure in the solid state. Each vanadium atom in the centrosymmetric dimer is coordinated in a trigonal-bipyramidal geometry, with a terminal tolylimido ligand and a bridging aryloxide group occupying the apical sites. There is a decided asymmetry in the V-0-V bridge bonding. Crystal data for 6: monoclinic, 12/c; a = 24.937 ( 5 ) , b = 10.790 ( 2 ) , c = 16.662 (3) A; 0 = 97.18 (2)'; Z = 8.
Although a number of vanadium(V) organoimido complexes are now known,' these species are generally insular and lack a systematic derivative chemistry. W e now report that trichloro@-tolylimido)vanadium(V), V ( N ~ O I ) C Ican ~ , ~be readily functionalized to afford a variety of alkoxide, aryloxide, and organometallic derivatives of (p-tolylimido)vanadium(V). The wide range of compounds accessible in this series has allowed us to begin to delineate the influence of various coordination environments on the 51VNMR characteristics of (organoimido)vanadium(V) complexes. Correlations between the 51VNMR results and the electronic spectra of these species are examined with the aid of extended Hiickel calculations and provide an illustrative comparison to related vanadium(V) complexes of oxo and alkylimido ligands. W e also report the molecular structure of a dimeric TKansas State University. f University of Kansas.
0002-7863/87/1509-7408$01 .50/0
(2,6-dimethylphenoxide) species, [V(Nt0l)(0Ar),Cl]~. A subsequent paper will describe various chelate derivatives of V(Ntol)CI, and the preparations of (p-tolylimido)vanadium(IV)
specie^.^ (1) (a) Burger, H.; Smrekar, 0.;Wannagat, U.Monatsh. Chem. 1964, 95, 292. (b) Slawisch, A. Z . Anorg. Allg. Chem. 1970, 374, 291. (c) Shihada, A. F. Z . Anorg. Allg. Chem. 1974, 408, 9. (d) Nugent, W. A.; Harlow, R. L. J . Chem. SOC.,Chem. Commun. 1979, 342. (e) Preuss, F.; Towae, W. Z . Naturforsch., B: Anorg. Chem., Org. Chem. 1981, 36B, 1130. (0Bradley, D. C.; Hursthouse, M. B.; Jelfs, A. N. M.; Short, R. L. Polyhedron 1983, 2, 849. (9)Nugent, W. A. Inorg. Chem. 1983,22,965. (h) Preuss, F.; Towae, W.; Kruppa, V.; Fuchslocher, E. 2.Naturforsch., B: Anorg. Chem., Org. Chem. 1984,39B, 1510. (i) Schweda, E.; Scherfise, K. D.; Dehnicke, K. Z . Anorg. Allg. Chem. 1985, 117. 6 ) Preuss, F.; Becker, H. Z . Naturforsch., B: Anorg. Chem., Org. Chem. 1986, 41B, 185. (k) Preuss, F.; Noichl, H.; Kaub, J. Ibid. 1986, 41B, 1085. (2) Maatta, E. A. Inorg. Chem. 1984, 23, 2560. (3) Wheeler, D. E.; Maatta, E. A,, to be submitted for publication.
0 1987 American Chemical Society
J . Am. Chem. SOC.,Vol. 109, No. 24, 1987 7409
(ArylimidoJvanadium Complexes
Results Syntheses and Properties. The synthesis of V(Ntol)CI3, 1, from VOCl, and p-tolyl isocyanate is readily accomplished in refluxing octane. A range of para-substituted phenylimido derivatives may
4
creasing electronic saturation provided by the strongly *-donating tert-butoxide groups. Likewise, an homologous series of 2,6-dimethylphenoxide derivatives of l has been prepared, as shown in eq 3-5 (Ar = 2,6-C6H3(CH3),). Aryloxide ligands are less efficient A donors 1
1 + HOAr (excess)
N 111
c , . - - vA IC'
-
+ HOAr
1
THF
THF
+ 3HOAr
CI
-1 be similarly prepared by using the appropriate aryl isocyanate as shown in eq 1. All of these (arylimido)vanadium(V) species OVC1,
+ p-XC,&NCO
Octane reflux
V(NC6H4X)C13 + COl
(1)
X = CH,, CF,, OCH,, F, C1, Br are intensely colored solid materials that decompose rather quickly upon exposure to the atmosphere; they can, however, be stored a t room temperature under nitrogen for extended periods of time. These trichloro complexes are moderately soluble in benzene and toluene, are considerably more soluble in methylene chloride and chloroform, and are quite soluble in coordinating solvents such as tetrahydrofuran. All of these species display excellent thermal stability: V(Ntol)Cl, may be conveniently purified by sublimation at ca. 130 OC Torr). The mass spectrum of 1 determined at 35 OC reveals only mononuclear isotopomers to be present. The structure of 1 in the solid state is not known; however, the degree of oligomerization of related imidovanadium(V) systems varies with the nature of the imido substituent. For example, while V(NSiMe3)C13 is monomeric in the solid state,li V(NI)C13 is dimeric with bridging chloride ligands4 The related complex V(NPh)Cl, is polymeric (with weak chloride bridges) in the solid state.5 V(Ntol)CI, undergoes a color change from dark purple to green upon dissolution in toluene; this observation most likely reflects an oligomeric [V(Ntol)C13], species dissociating into monomeric units in solution. V(Ntol)Cl, possesses a formal 12-electron configuration and reacts readily with Lewis bases such as T H F or PPh, to afford isolable addition complexes of the form V(Ntol)Cl,(L). The isolation of these monoadducts is somewhat surprising in view of the chemistry displayed by the isoelectronic VOCl, system, which typically forms bisadducts of the type VOC13(L),.6 It seems likely that pseudooctahedral bisadducts of the type V(Ntol)Cl,(L), can form in solution, and their instability to isolation may be attributable to the strong trans-influence exerted by organoimido ligands in 16-electron pseudooctahedral complexes.' It is also probable that the nature of the organoimido substituent influences the degree of Lewis base association in V(NR)CI, species. The chloride ligands in V(Ntol)CI, may be sequentially substituted by stoichiometric amounts of potassium tert-butoxide in THF solution to afford purple V(Ntol)Cl,(O-t-Bu), 2, orange V(Ntol)C1(0-t-B~)~, 3, and yellow V(Ntol)(O-t-Bu),, 4, as shown in eq 2. In the 'H N M R spectra of these organoimido alkoxides, V(Ntol)Cl,
+ nKO-t-Bu
THF
V(Ntol)Cl,-,,(O-t-Bu), 2 ( n = 1); 3 (n = 2); 4 (n = 3)
(2)
the resonances due to the aryl protons, the tolyl methyl group, and the 0-t-Bu protons all shift to progressively higher fields as the degree of substitution increases, presumably reflecting in(4) Beindorf, G.; Strahle, J.; Liebelt, W.; Weller, F. Z . Narurforsch., B Anorg. Chem., Org. Chem. 1980, 36B, 153. ( 5 ) Bradley, D. C.; Jelfs, A. N. M., personal communication. ( 6 ) Funk, H.; Weiss, W.; Zeising, M. Z . Anorg. Allg. Chem. 1958, 296, 36. (7) Chou, C. Y.; Huffman, J. C.; Maatta, E. A. Inorg. Chem. 1986, 25, 822.
V(Ntol)Cl,(OAr)(THF) 5
[V(Ntol)Cl(OAr)(pOAr)l, THF
6
(3) (4)
V(Ntol)(OAr), 7
than are alkoxide ligands, and thus the vanadium centers in the 2,6-dimethylphenoxide complexes should be relatively electron deficient as compared to their tert-butoxide analogues. The comparative electrophilicity of the aryloxide species is readily apparent in their 51V N M R spectra (vide infra) and is also manifest in the constitution of the mono- and bis(2,6-dimethylphenoxide) complexes: unlike the corresponding tert-butoxide species, the mono(ary1oxide) complex incorporates a ligating T H F molecule and the bis(ary1oxide) complex adopts a dimeric structure in which the vanadium atoms are bridged by two dimethylphenoxide ligands. All of the dimethylphenoxide complexes are very soluble in common organic solvents, including pentane, which renders them difficult to crystallize. As is the case with all of the organoimido complexes reported herein, exposure of the dimethylphenoxide derivatives to air results in their rapid decomposition, presumably via extensive hydrolysis. We have studied the controlled hydrolysis of V(Ntol)(OAr), by 'H and *'V N M R . Addition of H 2 0 (1 equiv) to a C6D6 solution of 7 results in relatively clean hydrolysis of the tolylimido ligand, forming p-toluidine and OV(OAr), (6(51V)= -51 1; fwhm = 20 Hz), along with a small amount of free 2,6-dimethylphenol, without any detectable intermediates (eq 6). 7 + H z O OV(OAr), tolNHz (6)
-
+
The identity of the OV(OAr), product has been confirmed by an X-ray crystal structure analysis.* Similarly, the controlled hydrolysis of [V(Ntol)Cl(OAr),], in C6D6affords p-toluidine and =)-363; fwhm = 54 Hz); significant amounts OVC1(OAr)z ( I ~ ( ~ ' V of OV(OAr), and free 2,6-dimethylphenol were also observed in the N M R spectra of this reaction. An homologous series of (trimethylsily1)methyl complexes has also been prepared as shown in eq 7. Although a variety of alkylating agents were examined (including RLi, RMgX, and R2Zn reagents), tractable alkyl complexes of (toly1imido)vanadium(V) were only obtained by using bis[(trimethylsilyl)methyl]magnesium. Complexes 8-10 are rare examples of va1
toluene + Mg(CH,SiMe,)z 00~V ( N ~ O ~ ) ( C H ~ S ~ M ~ , )(7) ,C~~-~
8 (x = 1); 9 (x = 2); 10 (x = 3)
nadium(V) organometallic^;^ it seems likely that our inability to isolate organometallic vanadium(V) derivatives from the reactions (8) Devore, D. D.; Takusagawa, F.; Maatta, E. A., unpublished results. (9) Apart from our CpV(Ntol)CI, and V(Ntol)(CH2SiMe3),C13-x species, the only well-characterized vanadium(V) organometallics known to us are the following. (a) CpVOX, (X = C1, Br): de Liefde Meyer, H. J.; Van der Kerk, G. J. M. Recl. Trau. Chim. Pays-Bas 1965, 84, 1418. (b) VO(CH2SiMe3)3: Mowat, W.; Shortland, A.; Yagupsky, G.; Hill, N. J.; Yagupsky, M.; Wilkinson, G. J . Chem. SOC.,Dalton Trans. 1972, 533. (c) VO(OR)CH3 (R = i-Pr, s-Bu, t-Bu): Lachowicz, A.; Thiele, K.-H. 2. Anorg. Allg. Chem. 1977, 431, 88. (d) Cp2VOC1: Holliday, A. K.; Makin, P. H.; Puddephatt, R. J. J . Chem. Soc., Dalton Trans. 1979, 228. ( e ) VO(0-i-Pr),Ph: Choukroun, R.; Sabo, S. J . Organomet. Chem. 1979, 182, 221. (f) VOC1,Ph: Thiele, K.-H.; Schumann, W.; Wagner, S.; Bruser, W. Z . Anorg. Allg. Chem. 1972, 390, 280. (g) Li[VO(O-t-Bu),(n-Bu)], VO(O-t-Bu),(CH2SiMe3): Preuss, F.; Ogger, L. Z . Naturforsch., B: Anorg. Chem., Org. Chem. 1982, 378, 957. (h) VOR, (R = mesityl): Seidel, W.; Kreisel, G.Z . Chem. 1982, 22, 113. (i) V(N-r-Bu)(O-r-Bu),R (R = Me, n-Bu, CH2SiMe3, mesityl), V(N-tBu)(O-t-Bu)R2 (R = mesityl): Reference lj. 6)(C5R,)VOX2 (R = H, CH,; X = C1, Br, Ph, OCH3): Herrmann, W. A,; Weichselbaumer, G.; Kneuper, H.-J. J . Organomet. Chem. 1987, 319, C21.
1410 J. Am. Chem. Soc., Vol. 109, No. 24, 1987
Deuore et ai.
Table I. Electronic Spectra of V(Ntol)CI, and Derivatives"
Table 11. *'V NMR Data for V(NtoiIC1, and Related Comnlexes" . complex 6("V) fwhm, Hz ' J S I ~ -Hz I~~. V(Ntol)(CH,SiMe,),' 1048 270b 94 V(Ntol)CI(CH2SiMd,),e 900 353 V(Ntol)CI,(CH,SiMe,)' 697 378 V (Ntol)CI,( PPh,) 392 700 V(Ntol)CI,(THF) 314 1900 V(Ntol)CI, 305 500 ,
A,,,,
nm
complex vis near-IR V(Ntol)CI, (1) 654 1040 V(Ntol)CldO-t-Bu) (2) 516 1052 V(Ntol)Cl 25'. Intensity measurements were made on a Syntex P2, diffractometer with graphite (002) monochromatized Mo K a radiation (A = 0.71069 A). A correction was applied for a small amount of decay observed in the intensities of two standard reflections throughout the period of data collection. Intensities were corrected for absorption30and Lorentz-polarization factors. Reflections with I,, < 0.2u(10) were reset to I,, = 0.2u(Io). All unique data were used in the subsequent refinement. The structure was solved by the heavy-atom method. All hydrogen atoms attached to the aryl rings were located in difference maps, but the methyl group hydrogens were not found. Therefore, all hydrogen atoms were placed in idealized positions and were included in structure factor calculations but were not included in the refinement. All positional and anisotropic thermal parameters of the non-hydrogen atoms were refined by full-matrix least-squares procedures. Calculations were performed on a Honeywell 66/6000 computer at the University of Kansas using programs in the DNA system of F. Takusagawa. The quantity minimized was Cw(lFoI - klFc1)2,where w refers to the weights and k is the scale factor (final value of k = 4.878 (4)). I n the early refinements, weights of w = 4F,2/u2(F,2) were used. In later refinements, weights were taken as l/uncw2,where uneW2 = u2 + 0.5AIFOl2+ 0.5B[(sin 0)/Al2; the values of A and B were obtained by least-squares minimization of the functions C(AF2- unew2)2 for 20 separate segments in IFo]and (sin B ) / A . Atomic scattering factors for all atoms and anomalous dispersion factors for V and CI were taken from the usual s o u ~ c e . ~A ' final difference Fourier _ _ . I _
I _ _ _
(30) North, A. C. T.; Phillips, D. C.; Matthews, F. S. Acta Crystallogr., Seer. A : Cryst. Phys., D g f r , , Theor. Gen. Crystallogr. 1968, 24, 351. (31) Cromer, D. T.; Waber, J. T. Internarional Tables f o r X-ray Crystnllography; Kynoch: Birmingham, England, 1974; Vol. IV.
J . Am. Chem. SOC. 1987, 109, 7416-7420
7416
synthesis showed no significant residual electron density; the largest peak was 0.34 e/A3. See Table VI for a summary of crystallographic data. Theoretical Calculations. Calculations were of the extended Hiickel type,” with programs locally modified and supplied by Prof. Keith Purcell. Values of bond lengths and bond angles employed were taken from structural data.’di7*32The V-C bond length was chosen to be the sum of their covalent radii (1.994 A), and an N-V-C angle of 106O was assumed. Values of Slater exponents, coefficients, and atomic orbital energies for elements with Z 5 17 were taken from the literature.27 The Slater exponents (coefficients in parentheses) for vanadium (chosen to be in the +3 oxidation state) were determined33to be as follows: 3d, 4.75 (0.498), 1.90 (0.655); 4s, 1.6 (1.0); 4p, 1.6 (1.0). Atomic orbital energies for vanadium (calculated by the method of Gray et al.34)employed in (32) (a) Scherfise, K. D.; Dehnicke, K.; Schweda, E. Z . Anorg. Allg. Chem. 1985, 528, 117. (b) Karakda, K.; Kuchitsu, K. Inorg. Chim. Acta 1975, 13, 113. (33) Richardson, J. W.; Niewport, W. C.; Powell, R. R.; Edgell, W. F. J . Chem. Phys. 1962, 36, 1057.
the calculations were Hdd= -12.55 eV, H , = -10.74 eV, and Hpp= -7.04 eV. Acknowledgment. This work was supported by the National Science Foundation (Grant CHE-8604359). D.D.D. thanks the Phillips Petroleum Corp. for a fellowship. The WM-400 N M R spectrometer employed in this work was purchased with the assistance of an NSF instrumentation award. W e are grateful to Professors K. F. Purcell and P. M. A. Sherwood for their aid in implementing the EHMO calculations. Supplementary Material Available: Tables of fractional coordinates of hydrogen atoms, anisotropic thermal parameters, complete bond distances and angles, and torsion angles (8 pages); listing of observed and calculated structure factor amplitudes (14 pages). Ordering information is given on any current masthead page. (34) Basch, H.; Viste, A,; Gray, H. B. Theor. Chim. Acta 1965, 3, 458.
Bridge Deprotonation of nido-2,3-RR’C2B4H6Carboranes and B5H9: A Kinetic Study Mark E. Fessler,lBThomas Whelan,lb James T. Spencer,Iband Russell N. Grimes* Contribution from the Department of Chemistry, University of Virginia, Charlottesville, Virginia 22901. Received May 19, 1987
Abstract: The heterogeneous reactions of the title compounds (R = alkyl, arylmethyl, or phenyl; R’ = R or H) with suspended N a H or KH in T H F to give M+[RR’C2B4H5-] + H2 were studied as a function of temperature, with determination of reaction rates from the rate of formation of H2. In all cases the kinetic rate law is pseudo-first order with linear plots of -In k l vs. 1/T, and the rate is independent of the amount of metal hydride present. Reactions with NaD in place of NaH give no detectable incorporation of deuterium into the carborane anion. The main trend observed is a moderate decrease in reaction rate as the sizes of R and R’ are increased, the effect being greatest in the bis(chromiumbenzy1)carborane complex [(C0)3CrPhCH2]2C2B4H6. The data are interpreted as reflecting primarily steric inhibition of the reaction by the R groups, except in the diphenyl derivative Ph2C2B4H6which exhibits very fast reaction rates at the higher temperatures measured (above -40 “C) and anomalously high activation energy (Ea) and low entropy of activation (AS*). In this instance, electron withdrawal by the phenyl groups via resonance and pronounced steric effects by the phenyls are proposed to account for the observed behavior.
A characteristic feature of most open-cage (non-closo) boranes and carboranes, and many of their metal-containing derivatives, is the presence of one or more three-center-bonded B-H-B groups on the open face of the molecule. These bridging hydrogens typically exhibit acidic behavior toward strong Lewis bases and can be removed to generate a conjugate base anion,2 e.g. B5H9
+ NaH
-
Na+B5H8- + H2
(1)
Rarely, however, can more than one proton per molecule be removed even under forcing conditions. As first shown long ago by Onak and c o - ~ o r k e r sthe , ~ nido-carborane 2,3-C2B,H8 and its C- and B-substituted derivatives are readily converted to the corresponding m o n ~ a n i o n(eq ~ , ~2 and Figure 1). The reactions proceed cleanly and quantitatively, as we have verified from high-resolution (115.8 M H z ) IlB N M R spectra of the anions (1) (a) Undergraduate research participant, University of Virginia, 1985-1987. (b) Present address: Department of Chemistry, Syracuse University, Syracuse, NY 13244. (2) Greenwood, N. N. The Chemistry. of. Boron; Pergamon: Oxford, 1973; Chapter 4; and references therein. (3) (a) Onak, T.; Dunks, G. B. Inorg. Chem. 1966, 5 , 439. (b) Onak, T.; Lockman, G.; Haran, G. J . Chem. Soc., Dalton Trans. 1973, 21 15. (4) Savory, C. G.; Wallbridge, M. G. H. J . Chem. Soc., Dalton Trans. 1974, 880.
-
produced. The neutral carboranes are readily accessible via the C2B4Hg + M+H-
M’CZBdH7-
+ H2
(2) base-promoted reaction of B5H9with alkynesS and constitute a large carborane family with a steadily increasing role in synthesis.6 In recent years, studies of C,C’-disubstituted R2C2B,H6derivatives have disclosed a variety of synthetically useful processes based on these compounds (e.g., metal-induced oxidative fusion to form R4C4B8H8c l ~ s t e r s , 6alkyne ~ ~ incorporation into the cage,8 and cage expansi~n~~’~). In the course of our research we have prepared, as reagents for synthetic purposes, a number of nido-RR’C2B4H6species in (5) (a) Onak, T.P.; Williams, R. E.; Weiss, H. G. J. A m . Chem. SOC. 1962,84, 2830. (b) Hosmane, N. S.; Grimes, R. N. Inorg. Chem. 1979, 18, 3294. (c) Maynard, R. B.; Borodinsky, L.; Grimes, R. N. Inorg. Synth. 1983, 22, 211. (6) (a) Grimes, R. N. Pure Appl. Chem. 1987, 59, 847. (b) Spencer, J. T.; Pourian, M. R.; Butcher, R. J.; Sinn, E.; Grimes, R. N. Organometallics 1987, 6 , 335 and references therein. (7) Grimes, R. N. Adv. Inorg. Radiochem. 1983, 26, 55 and references
therein.
(8) Mirabelli, M. G. L.; Sneddon, L. G . Organometallics 1986, 5 , 1510. (9) Wermer, J. R.; Hosmane, N. S.; Alexander, J. J.; Siriwardane, U.; Shore, S. G. Inorg. Chem. 1986, 25, 4351. (10) Beck, J. S.; Kahn, A. P.; Sneddon, L. G. Organomefallics 1986, 6 , 2552.
0002-7863/87/ 1509-7416%01.50/0 0 1987 American Chemical Society
