J . Am. Chem. SOC.1992, 114, 748-751
148
J = 4.8, 12.4, 1 H, H-le), 2.90 ( d d , J = 4.6, 11.9, 1 H, H-5e), 3.72 (ddd, J = 3.0, 5.1, 11.7, 1 H, H-4), 3.85 (br s, 1 H, H-3); I3C NMR (D,O) 6 15.4 (CH3), 35.5 (C-2), 44.8, 45.7 (C-1, (2-5). 67.0, 72.6 (C-3, C-4);
6 - ~ w r o - 1 , 4 , 5 , 6 - t e h P d e o x y - l , ~ ~ ~ - l(15): y ~ t oHydrogenolysis i of 11 resulted in a mixture of 14 (52% yield) and 15 (1 1% yield) after column chromatography on silica gel ('PrOH/H20/NH40H, l4:l:l); 'H NMR (D,O) 6 1.50 (app q, J = 12.0, 1 H, H-3a), 1.66 (app dt, J = 3.8, 12.4, 1 H, H-3e), 2.69 (dd, J = 1.3, 14.3, 1 H, H-6a), 2.91-2.83 (dddd, J = 3.0, 5.7, 12.2, 25.3, 1 H, H-2), 3.03 (dd, J = 2.8, 14.3, 1 H, H-6e), 3.80 (ddd, J = 3.0, 7.7, 11.6, 1 H, H-4), 3.84-3.81 (m, 1 H, H-5), 4.37 (ddd, J 5.7, 9.7, 47.2, 1 H, H-l), 4.46 (ddd, J 3.0, 9.7, 47.2, 1 H, 5.9), 49.2 (C-6), 54.6 (C-2, H-1); "C NMR (D,O) 6 29.4 (C-3), 'JC-F 'Jc+ = l8.l), 67.6,69.8 ((2-4, (2-5). 87.00 ((2-1, IJc+ = 165.3); HRMS ( M - H)+ calcd 150.0930, found 150.0923. (2S)-Metbyl-1,2,5-tdeoxy-l,5-imino-~-ribitol(16): 90% yield; IH NMR (D20)6 0.91 (d, J = 7.0, 3 H, CH3), 1.77-1.82 (m, 1 H, H-2), 2.45 (t, J = 12.4, 1 H, H-la), 2.67 (t, J = 11.7, 1 H, H-5a), 2.70 (dd,
HRMS (M - Cs)+ calcd 264.0001, found 264.0003. 1,2,5-Trideoxy-1,5-imino-~-erythritol(17): 97% yield; lH NMR (DzO) 6 1.51 (m, 2 H, H-2), 2.55 (ddd, J = 4.8, 7.6, 13.1, 1 H, H-l), 2.67 (dd, J 3.0, 13.4, 1 H, H-5), 2.90 (dd, J = 5.7, 13.4, 1 H, H-5), 2.86-2.96 (m,1 H, H-l), 3.67 (dt, J = 2.5, 5.9, 1 H, H-4), 3.74 (ddd, J = 3.0, 4.6, 7.6, 1 H, H-3); 13CNMR (D20) 6 29.9 (C-2), 41.9 (C-l), 48.1 (C-5), 68.8, 69.3 (C-3, (2-4); HRMS (M+) calcd 117.0790, found 117.0785.
Acknowledgment. This research was supported by the NIH (GM44154).
[ Tris( pyrazolyl)hydroborato]magnesium Alkyl Derivatives:
Reactivity Studies Runyu Han and Gerard Parkin* Contribution from the Department of Chemistry, Columbia University, New York. New York 10027. Received July 1 , 1991
Abstrsct The reactivity of a series of 4-coordinate [tris(pyrazolyl)hydroborato]magnesium alkyl derivatives, (q3-HB(3-Bu'pz),]MgR and (q3-HB(3,5-Me2pz)31MgR(3-Bu'pz = 3-C3N2ButH2, 3,5-Me2pz = 3,5-C3N2MezH;R = CH3, CH2CH3,(CH2),CH3, MgR CH(CH,),, C(CH3),, CH=CH2,C6H5, CH2SiMe3),has been investigated. The complexes ( ~ ~ - H B ( 3 , 5 - M e ~ p z ) ~ ) undergo ligand redistribution reactions, analogous to the Schlenk equilibrium, to give the 6-coordinate sandwich complex {$HB(3,5-Me2pz),),Mg. In contrast, the 4-coordinate magnesium alkyl derivatives supported by the more sterically demanding tris(3-tert-butylpyrazolyl)hydroborato ligand, (?3-HB(3-Bu'pz)3}MgR, are stable with respect to the formation of ($-HB(3B ~ ' p z ) ~ ) ~ MThe g . alkyl complexes ( $ - H B ( ~ - B u ' ~ z ) ~ } Mare ~ Ruseful precursors for a variety of other 4-coordinate complexes, including {$-HB(3-Butpz)3)MgX (X = m C 6 H 5 , C%CSiMe3, OEt, O w , OBu', OPh, OCH2SiMe3,OSiMe,, OOBu', NHPh, SH, SCH3,CI, Br, I, NCO, NCS). C 0 2inserts into the Mg-C bond of ( T ~ - H B ( ~ - B U ' ~ Z ) ~ )toMgive ~ C the H ~Vl-aetato complex (Q~-HB(~-Bu'~z)~}M~(~~-OC(O)CHS). In contrast, the reactions with the ketones CH3C(0)CH3 and CH3C(0)But do not result in insertion to give the alkoxide derivatives, but preferentially give the enolate complexes (~3-HB(3-Bu'pz)3)Mg{~'-OC(==CH2)CH3) and (q3-HB(3-B~tp~)3)Mg(~1-OC(=CH2)Bu'), accompanied by the elimination of methane. Insertion of O2 into the Mg-R bond of the complexes (v3-HB(3-Bu'pz)3)MgR(R = CH3, CH2CH3, CH(CHJ2, C(CHJ3) results in formation of the alkylperoxo derivatives { ~ ' - H B ( ~ - B U ' ~ Z ) ~ J M ~which O O Rhave , been characterized by the use of 1 7 0 N M R spectroscopy. In contrast, the reaction of the magnesium (trimethylsily1)methyl complex (q3-HB(3-Bu'pz),)MgCH2SiMe3 with O2gives the trimethylsiloxide as a result of facile cleavage of the Si-C bond upon autoxidation. The molecular derivative ($-HB(3-Butpz)g)MgOSiMe3 structures of (v3-HB(3,5-Me2pz),l2Mg and (q3-HB(3-Bu' z),lMgCI have been determined by X-ray diffraction. (q3-HBb = 10.223 (3) A, c = 10.773 (2) A, a = 63.92 (3)O, fi = 85.24 (3,5-Me2pz),J2Mgis triclinic, Pi (No. 2), a = 8.837 (3) (2)O, y = 79.87 (2)", V = 860.4 (4) A', Z = 1. (03-HB(3-Bu'pz),)MgC1 is orthorhombic, Pnma (No. 62), a = 16.048 (7) A, b = 16.006 (3) A, c = 9.840 (1) A, V = 2527 (1) A3, Z = 4.
1,
Introduction We have recently reported the syntheses and structures of a series of 4-coordinate organomagnesium complexes ($-HB(3B ~ ' p z ) ~ l M g(A) R and (q3-HB(3,5-Me2pz),)MgR (B) (3-Butpz = 3-C3N2ButH2; 3,5-Me2pz = 3,5-C3N2Me2H)]that are stabilized by coordination of tris(pyrazoly1)hydroborato ligands: as illus-
[tris(pyrazolyl)hydroborato]magnesium alkyl derivatives are soluble in noncoordinating hydrocarbon solvents (e.g., benzene) and possess valuable spectroscopic handles, in the form of the resonances due to the tris(pyrazoly1)hydroborato ligands, that are ideal for monitoring reactions. Here we report our studies of
trated in Figure 1.
(3) The simple model of the Schlenk equilibrium (2RMgX a RzMg + MgX2) for describing the composition of Grignard reagents is complicated by a variety of factors including (i) the formation of complexes of each component with either solvent, reactant, or product, (ii) the formation of dimeric (or higher order) species, and (iii) the presence of ionic species. (a) Kharasch, M. S.; Reinmuth, 0. Grignard Reactions of Nonmetallic Substances; Prentice-Hall: New York, 1954. (b) Ashby, E. C. Pure Appl. Chem. 1980,52,545-569. (c) Ashby, E. C. Q. Rev. 1967,259-285. (d) Ashby, E. C.; Laemmle, J.; Neumann, H. M. Acc. Chem. Res. 1974, 7, 272-280. (e) Wakefield, B. J. Pure Appl. Chem. 1966, I, 131-156. ( f ) Toney, J.; Stucky. G. D. J. Organomer. Chem. 1971, 28, 5-20. (g) Ashby, E. C.; Smith, M. G. J. Am. Chem. SOC.1964, 86, 4363-4370. (h) Ashby, E. C.; Becker, W. E. J. Am. Chem. SOC.1963.85, 118-1 19. (i) Guggenberger, L. J.; Rundle, R. E. J. Am. Chem. SOC.1968,90,5375-5378. (i)Spek, A. L.; Voorbergen, P.; Schat, G.; Blomberg, C.; Bickelhaupt, F. J. Organomer. Chem. 1974, 77, 147-151. (k) Schlenk, W.; Schlenk, W., Jr. Ber. 1929, bZB, 920-924. (I) Evans, W. V.; Pearson, R. J. Am. Chem. SOC.1942, 64, 2865-2871. (m) Dessy, R. E.; Handler, G. S. J. Am. Chem. SOC.1958, 80, 5824-5826.
In contrast to Grignard reagents, which are well-known t o (i) exist in solution as a complex mixture of species (e.g., the Schlenk equilibrium) and (ii) exhibit a variety of structures in the solid state,3 the organomagnesium complexes illustrated in Figure 1 exist as well-defined 4-coordinate monomeric complexes both in the solid state and in solution. Furthermore, the solvent-free (1) Han, R.; Parkin, G. Organometallics 1991, 10, 1010-1020. (2) (a) Trofimenko, S.Acc. Chem. Res. 1971,4, 17-22. (b) Trofimenko, S. Chem. Rev. 1972, 72,497-509. (c) Trofimenko, S.Prog. Inorg. Chem. 1986,34, 115-210. (d) Shaver, A. Comprehensive Coordination Chemistry; Wilkinson, G., Gillard, R. D., McCleverty, J. A,, Eds.; Pergamon Press: Oxford, 1987; Vol. 2, pp 245-249. (e) Shaver, A. J. Organomet. Chem. Library 1977.3, 157-188. ( f ) Niedenzu, K.; Trofimenko, S. Top. Curr. Chem. 1986, 131, 1-37.
0002-7863/92/1514-748$03.00/0
0 1992 American Chemical Society
/Tris(pyrazolyl)hydroborato]magnesiumAlkyl Derivatives
Figure 1. Monomeric [tris(pyrazolyl)hydroborato]magnesium alkyl complexes.
" b Figure 2. Molecular structure of (s3-HB(3,5-Me2pz),J2Mg.
[tris(pyrazolyl)hydroborato]magnesium alkyl derivatives in order to assess the reactivity of the magnesium-carbon bond in a well-defined 4-coordinate environment. Results and Discussion The monomeric [tris(pyrazoly1)hydroboratolmagnesium alkyl derivatives (q3-HB(3-Butpz)3)MgR and (q3-HB(3,5-Mqpz)3)MgR (R = CH3, CH2CH3, (CHd3CH3, CH(CHs)z, C(CH3)3, CHzSiMe3,CH=CHz, C6H5) were obtained as described previously by the metathesis of R2Mg with M{HB(3,5-R2pz)3) (3,5-R2pz = 3-Butpz, 3,5-Me2pz;M = K, Tl), as shown in eq 1.'
-WRI
R2Mg + M ( H B ( ~ , ~ - R z P Z ) ~ )
(13-HB(3,5-Rz~z)3)MgR(1) The reactivity of the complexes (q3-HB(3,5-Rzpz),)MgRis described below under the general classifications of (i) ligand redistribution, (ii) metathesis, and (iii) insertion reactions. Ligand Redistribution Reactions. In view of the fact that Grignard reagents exist in solution as a complex mixture of species as a result of facile ligand redistributionreactions, e.g., the Schlenk eq~ilibrium,~ we have investigated the possibility of similar ligand redistribution reactions for the [tris(pyrazolyl)hydroborato]magnesium alkyl complexes, (q3-HB(3,5-R2pz)3}MgR.Thus, we have observed that although solutions of the tris(3,5-dimethylpyrazoly1)hydroborato derivatives (q3-HB(3,5-Me2pz)JMgR (R = CH3, CHzCH3,(CHZ)$H3, CH2SiMe3,CH(CH3)2,C(CH&, CH=CH2, C6H5) are stable at room temperature, heating to 80-120 "C results in ligand redistribution and the formation of the 6-coordinate sandwich complex (q3-HB(3,5-Mezpz)3)zMg (eq 2) *
The reactions only proceed to ca. 90% completion, presumably arriving at equilibrium. The molecular structure of (q3-HB(3,5Me2pz)J2Mghas been determined by X-ray diffraction, as shown in Figure 2. Selected bond lengths and angles are presented in Tables I and 11. The two tris(pyrazoly1)hydroborato ligands adopt
J. Am. Chem. SOC.,Vol. 114. No. 2, 1992 149 Table I. Selected Bond Lengths for (v3-HB(3,5-Me2pz),J2Mg(A) Mg-N(l2) 2.192 (2) Mg-N(22) 2.169 (2) Mg-N(32) 2.197 (3) Mg-N(12') 2.192 (2) Mg-N(22') 2.169 (2) Mg-N(32') 2.197 (3) N(l1)-N(12) 1.375 (3) N(l1)-C(l1) 1.353 (3) N(1l)-B 1.547 (4) N(12)C(13) 1.341 (3) N(21)-N(22) 1.375 (3) N(21)-C(21) 1.353 (3) N(2 1)-B 1.544 (4) N(22)-C(23) 1.337 (4) N(31)-N(32) 1.375 (3) N(31)-C(31) 1.348 (5) N(31)-B 1.543 (4) N(32)C(33) 1.340 (5) C(l1)-C(12) 1.368 (4) C( 1 1)-C( 14) 1.505 (4) C(12)-C(13) 1.386 (4) C( 13)-C( 15) 1.496 (4) C(21)-C(22) 1.355 (5) C(21)-C(24) 1.494 (4) C(22)C(23) 1.383 (4) C(23)-C(25) 1.493 ( 5 ) C(31)C(32) 1.370 ( 5 ) C(31)-C(34) 1.497 (5) C(32)C(33) 1.376 (6) C(33)-C(35) 1.499 (4) Table 11. Selected Bond Angles for 85.6 (1) N( 12)-Mg-N(22) 85.6 (1) N ( 22)-Mg-N( 32) 94.4 (1) N(22)-Mg-N( 12') 94.4 (1) N ( 12)-Mg-N(22') 94.4 (1) N (32)-Mg-N(22') 93.0 (1) N ( 12)-Mg-N(32') N (32)-Mg-N( 32') 180.0 85.6 (1) N(22')-Mg-N(32')
I I I , - H B ( ~ , ~ - M ~ , P Z ) ~(deg) J,MR N(12)-Mg-N(32) 87.0 (1) N(12)-Mg-N(12') 180.0 N(32)-Mg-N(12') 93.0 (1) N(22)-Mg-N(22') 180.0 N(12')-Mg-N(22') 85.6 (1) N(22)-Mg-N(32') 94.4 (1) N(12')-Mg-N(32') 87.0 (1)
a mutually staggered conformation, and the overall coordination geometry about the centrosymmetric magnesium center is trigonally distorted octahedral. ($-HB(3,5-Me2pz)3)zMgcan also be readily prepared by the reaction of K(HB(3,5-Me2pz)Jwith MgBr2. Thus, coordination of two tris(dimethylpyrazoly1)hydroborato ligands to magnesium does not result in particularly excessive steric interactions, which accounts for the facile redistribution reaction described above. In contrast to the facile formation of {q3-HB(3,5-Me2pz)3)2Mg from (~~-HB(3,5-Me~pz)~)MgR, solutions of the tris(3-tert-b~tylpyrazoly1)hydroborato derivatives (q3-HB(3-Butpz)3)MgRin benzene are thermally stable. For example, solutions of (q3-HB( 3 - B d p ~ ) ~ ) M g cshow H ~ no evidence of decomposition after 7 days at 120 "C. This marked difference between (q3-HB(3Bu'pz),)MgR and (q3-HB(3,5-Mezpz)3)MgRderivatives is undoubtedly a consequence of the sterically demanding environment created by the ~~-HB(3-Bu'pz)~ ligand that disfavors the formation of the bis complex ( $ - H B ( ~ - B u ' ~ z ) ~ ) ~Indeed, M ~ . the tris(3tert-butylpyrazoly1)hydroborato ligand has been described as a "tetrahedral enforcer" due to its ability to effectively restrict a metal center to a maximum of 4-coordination! Thus, whereas the complexes (q3-HB(3,5-Me2pz)3JMgR undergo ligand redistribution reactions that are analogous to the Schlenk equilibrium, the more sterically demanding tris( 3-tert-butylpyrazoly1)hydroborato derivatives (q3-HB(3-Bu'pz),)MgRare not subject to such transformations. Such an observation is of particular relevance with regard to other studies (vide infra), and hence we have concentrated our efforts on the more sterically demanding (q3HB( 3-Butpz),)MgR system. Metathesis Reactions. The alkyl derivatives (q3-HB(3Bu'pz),)MgR are useful precursors to a wide variety of other derivatives as a result of metathesis of the magnesiumalkyl bond. Reactions of { $ - H B ( ~ - B U ' ~ Z ) ~ )with M~R protic reagents, e.g., RC=CH (R = Ph, SiMe3), ROH (R = Et, Pr', But, Ph, CH2SiMe3,SiMe3), Bu'OOH, PhNH?, CH3SH, H2S and HCl, are accompanied by elimination of the alkane and the formation of the corresponding magnesium derivative as shown in Scheme (4) The "tetrahedral enforcer" nature of the q,-HB(3-B~'pz)~ ligand was suggested for metals of similar size to the first-row transition elements." Although this is generally observed, we note that there are exceptions to this {q3-HB(3-Bu'pz)3)suggestion, namely (q'-HB(3-Bu'-5-Mep~)~]Co(q~-O~)$~ C U ( ~ ~ - O ~ Nand O ){~'-HB(~-BU'~~)~]N~(~*-O~NO)." .~ (a) Trofimenko, S.; Calabrese, J. C.; Thompson, J. S . Inorg. Chem. 1987, 26, 1507-1514. (b) Egan, J. W., Jr.; Haggerty, B. S.; Rheingold, A. L.; Sendlinger, S. C.; Theopld, K. H. J . Am. Chem. SOC.1990, 112, 2445-2446. (c) Han, R.; Parkin, G.J . Am. Chem. SOC.1991, 113, 9707-9708.
150 J. Am. Chem. SOC.,Vol. 114, No. 2, 1992
Han and Parkin
Scheme I
K-
\
=.?.?U'
\
-
ROH
H-
( R = Et, Pr', Bu', Ph, SiMq) a
-
-
/
v
/
4 %
4
/
B % J+ 2g J
4CH3
(R
-
CH,, Bu') -CHI
\
PY
-vn,
I. The molecular structure of the chloride complex (q3-HB(3MgCH, with trimethylsilyl derivatives Me,SiX (X = C1, Br, I, Bu'pz),)MgCl is shown in Figure 3, confirming the monomeric NCS, NCO) give (q3-HB(3-Bu'pz),]MgX and Me4Si. For the nature and q3-coordination of the tris(pyrazoly1)hydroborato reactions of (q3-HB(3-Butpz),]MgCH3with RI (R = CH,, ligand. Selected bond lengths and angles for (q3-HB(3CH,CH,) to give (q3-HB(3-Bu'pz)3)MgI,the alkane coupling Bu'pz),}MgCl are given in Tables I11 and IV. products RCH, were also observed by IH NMR spectroscopy. The reaction of (q3-HB(3-Bu'pz),)MgCH3 with acetone gives The reaction between (q3-HB(3-Butpz),)MgCH3and CH,I has the enolate complex (q3-HB(3-Butpz)3)Mg(q1-OC(=CH2)CH3) also been examined using ],CH31. Significantly,the reaction with and CH4. The clean formation of the enolate complex is not I3CH3I demonstrates that, in addition to alkylation (to give expected on the basis of conventional Grignard reactions with (q3-HB(3-Bu'pz),)MgIand I3CH3CH3),there is also a competitive acetone, in which the alkoxide derivative (q3-HB(3-Bu'pz),)metathesis process involving alkyl exchange (to give {q3-HB(3MgOC(CH,), should be formed. However, magnesium enolate Bu'pz),]Mgl3CH3 and CH,I), as shown in Scheme 111. complexes have previously been isolated for ketones with sterically The observation of competitive alkyl exchange is supported by demanding substituents, e.g., ButC(0)EtS and (2,4,6the reaction of (~-'-HB(~-BU'~~)~JM~CH~CH~ and CH31,in which Me3C6H2)C(0)CH3.6 The formation of (q3-HB(3-Butpz),)Mgalkyl exchange giving (q3-HB(3-Bu1pz),]MgCH3is observed to (q'-OC(=CH,)(CH,)J represents a unique example of a magoccur concomitant with the irreversible formation of (q3-HB(3nesium enolate derived from acetone. Similarly, the reaction of Bu'pz),)MgI. To our knowledge, alkyl exchange has not previously (q3-HB(3-Bu'pz),)MgCH3with CH3C(0)Butgives the enolate been observed to occur between Grignard reagents and simple alkyl complex (q3-HB(3-Bu'pz)3)Mg(q1-OC(=CH,)(Bu')]. The NMR halides' although there is indirect evidence for alkyl exchange (as and IR data of (q3-HB(3-Bu'pz),)Mg(q~-OC(=CH2)(CH3)} and determined by the organic products after quenching with C 0 2 ) (q3-HB(3-Bu'pz),)Mg(q1-OC(=CH2)(Bu')J are particularly with more complex derivatives.8 The observation of alkyl excharacteristic of enolate derivatives. Specifically for (q3-HB(3change in the reaction of (q3-HB(3-Bu1pz)3]MgCH3 with CH31 Butpz),)Mg(q1-OC(=CH2)(CH,)], vC4 is observed at 1620 cm-' is reminiscent of the a-bond metathesis exchange process reported in the IR spectrum and the olefinic resonances (OC(=CH,)(CH,)) for (qs-CsMeS)2ScCH,.9 and (OC(=CH,)(CH,)J are observed at 6 83.1 and 161.9, reThe reactions of (q3-HB(3-Butpz),JMgCH3with aralkyl halides spectively, in the I3C NMR spectrum. C6HSCH2X(X = c1, Br, I) also result in the clean formation of Metathesis reactions are also observed with nonprotic reagents (q3-HB(3-Bu'pz),]MgX. However, significant quantities of bisuch as dimethyl disulfide, alkyl halides, trimethylsilyl derivatives, benzyl (C6HsCH2CH2C6HS) are observed in addition to the and halogens as shown in Scheme 11. Thus, (q3-HB(3product of coupling with the methyl group (C6H,CH2CH3),inB U ' ~ Z ) ~ ) M reacts ~ C H with ~ a variety of alkyl and aralkyl halides dicative of radical processes.I0 Support for this suggestion is (RX) at ca. 100-140 O C to give the halide derivative (q3-HB(3Bu'pz),)MgX. Similarly, the reactions of (q3-HB(3-Butpz),)(5) Willard, P. G.; Salvino, J. M. J . Chem. SOC.,Chem. Commun. 1986, 153-154. (6) Pinkus, A. G.; Lindberg, J. G.; Wu, A.-B. Chem. Commun. 1969, 135c-1351.
(7) Gilman, H.; Jones, H. L. J . Am. Chem. SOC.1929, 51, 2840-2846. (8) (a) Kharasch, M. S.; Fuchs, C. F. J . Org. Chem. 1945, 10, 292-297. (b) Kharasch, M. S.; Lambert, F. L.; Urry, W. H. J . Org. Chem. 1945, 10, 298-306. (9) Thompson, M. E.; Baxter, S. M.; Bulls, A. R.; Burger, B. J.; Nolan, M. C.; Santarsiero, 8. D.; Schaefer, W. P.; Bercaw, J. E. J. Am. Chem. SOC. 1987, 109, 203-219.
/Tris(pyrazolyl)hydroborato]magnesiumAlkyl Derivatives
J . Am. Chem. SOC.,Vol. 114, No. 2, 1992 751 Table IV. Selected Bond Angles for I ~ ' - H B ( ~ - B u ' D ~ ) ~ J(deal M~CI CI-Mg-N(l2) 121.4 (2) Cl-Mg-N(22) 123.4 (1) N(12)-Mg-N(22) 93.7 (1) Cl-Mg-N(22') 123.4 (1) N(12)-Mg-N(22') 93.7 (1) N(22)-Mg-N(22') 93.3 (2)
of 53 Hz being clearly indicative of a one-bond coupling. Furthermore, support for the ql-coordination mode of the acetato ligand is provided by the X-ray diffraction study of the zinc analogue, (q3-HB(3-Bu'pz)3)Zn(q'-02CCH3).14 Insertion reactions of {q3-HB(3-Bu'pz),}MgRare also observed with dioxygen. Thus, treatment of the alkyl complexes (q3-HB(3-Bu'pz)JMgR (R = CH3, CH2CH3, CH(CH3)2, C(CH3)3) with excess O2at room temperature results in formation of the alkylperoxo complexes (q3-HB(3-Bu'pz)3)MgOOR(eq 4). The
Figure 3. Molecular structure of (~3-HB(3-Bu'pz)3)MgCl, Table 111. Selected Bond Lengths for I$-HB(3-Butpz),)MgC1
Mg-C1 Mg-N(22) N(l1)-N(12) N(1I)-B N(21)-N(22) N(21)-B C(ll)-C(12) C(13)-C(14) C(14)-C(16) C(21)-C(22) C(23)-C(24) C(24)-C(26) B-N(21')
2.262 (2) 2.100 (3) 1.379 (6) 1.542 (8) 1.376 (4) 1.538 (5) 1.357 (10) 1.510 (9) 1.535 (7) 1.363 (6) 1.518 (6) 1.536 (7) 1.538 ( 5 )
Mg-N(12) Mg-N(22') N(ll)-C(ll) N(12)-C(13) N(21)-C(21) N(22)-C(23) C(12)-C(13) C(14)-C(15) C(14)-C(16') C(22)-C(23) C(24)-C(25) C(24)-C(27)
(A)
2.097 (5) 2.101 (3) 1.338 (8) 1.351 (7) 1.328 (5) 1.345 ( 5 ) 1.375 (10) 1.530 (9) 1.535 (7) 1.387 (6) 1.525 (6) 1.512 (7)
xovided by the observation that the reaction of cyclopropylmethyl xomide with {q3-HB(3-Bu'pz),)MgCH, results in ring opening ind the formation of the homoallyl derivative CH2=CHCH2CH2Br." The formation of products derived from ring-opening *eactionsof cyclopropylmethyl halide derivatives has previously Deen proposed to be a test for radical processes.12 In addition :o the nature of the products of the reactions of {q3-HB(3Bu'pz),]MgCH3 with alkyl and aralkyl halides, the qualitative rates if the reactions are also consistent with radical processes. Thus, 'or the alkyl iodides (CH31, CH3CH21,(CH3)2CHI,(CH3)3CI) .he increasingorder of reactivity is primary C secondary C tertiary, ind for the benzyl halides C6H,CH2X the order is chloride < xomide = iodide.', Insertion Reactions. Although the anticipated insertion reaction, .ypical of Grignard reactivity, was not observed between (q3HB(3-Butpz),)MgCH3and acetone to give the alkoxide derivative q3-HB(3-Bu'pz)3JMgOBu', clean insertion of C 0 2 to give the icetato complex was observed (eq 3). However, this reaction
reactions of the derivatives {q3-HB(3-Bupz),)MgR(R = CH2CH3, CH(CH3)2,C(CH3),) with O2are both instantaneous (
