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The carbonylation chemistry of [ ( ~ i l o x ) ~ T a H (1)~ tracks ]~ the critical sequence of complicated reactions pertaining to the F-T mechanism (deoxygenation, H-C and C-C bond formation) and provides alternative views of certain heterogeneous transformations. Since 2 is formed directly, the generation of (CH2)adsvia Htransfer concomitant with or prior to C - O bond scission must still be c o n ~ i d e r e d ;the ~ ~ dissociative adsorption of CO may not be necessary. Most importantly, a C - 0 bond has been broken, reformed, and broken again in the conversion of 1 to 4.,' Extrapolating to heterogeneous processes, oxygenated surfaces may serve as reservoirs for C H , CH,, and, presumably, CH332functionalities via (OCH)ads,33(OCH2)ah.34and (OCH3)ads. Methylene units adsorbed on actual F-T surfaces are therefore not constrained to be solely metal-bound. Further mechanistic studies and characterizations of thermal, hydrogenation, and other carbonylation products are currently being undertaken. Acknowledgment. Support from the Air Force Office of Scientific Research, Cornell University, Chevron Research Company, and the National Science Foundation (CHE-8308272) is gratefully acknowledged. We thank Mark M . Banaszak Holl for experimental assistance and the N S F and N I H for support of the Cornell N M R Facility.
Figure 1.
Structure of the cation of [($-C5H5)Re(NO)(PPh3)Selected bond lengths (A) and angles (deg): Re-I, 2.678 (1); Re-P, 2.385 (3); Re-N, 1.740 (9); N-0, 1.20 (1); I-CI, 2.18 (1); CI-Si, 1.88 (2); I-Re-P, 91.82 (9); I-Re-N, 97.0 (4); P-Re-N, 91.1 (3); Re-N-0, 177 (1); Re-I-CI, 102.5 ( 5 ) ; I-CI-Si, 114.5 (9).
(ICH2Si(CH3)3]tBF4'.(CH2C12),, (4d-(CH2CI2),5 ) .
Of all of the common organic functional groups, alkyl halides (RX) have by far the least developed coordination To our knowledge isolable 1:l adducts are unknown, although the has been bis(methy1 iodide) complex [(H)21r(PPh,)2(ICH3)2]+Xrecently described by Crabtree.' The lack of stable alkyl halide complexes has generally been attributed to poor Lewis basicity
and/or the availability of facile decomposition pathways such as oxidative addition. In this communication, we report the synthesis and isolation of alkyl iodide complexes of the formula [($C,H,)Re(NO)(PPh,)(IR)]+BF4-and other data that suggest that alkyl halide complexes may be far more accessible than previously realized. Importantly, the coordination of alkyl halides to metals provides a new generation of leaving groups that can be easily modified and, as in the reported examples, rendered chiral. We recently reported that the reaction of methyl complex ($-C5H5)Re(NO)(PPh3)(CH3)(1) and HBF,.Et20 (CH2CI2,-78 "C) gave a reactive intermediate (stable to -20 "C) formulated as the chiral pyramidal Lewis acid [($-C,H,)Re(NO)(PPh3)]+BF4- (2) or the CH,Cl, adduct [($-C,H,)Re(NO)(PPh,)(CICH,Cl)]+ BF4- (3).4 Subsequent I3C N M R experiments have provided good evidence for coordinated CH2C12.4b Hence, the reaction of 1 and HBF,.Et,O was followed by addition of alkyl iodides R I (3.0 equiv, Scheme I). New products formed upon warming (-40 to 0 "C, ca. 95%, 31PNMR). Workup gave alkyl iodide complexes [(~5-C,H,)Re(NO)(PPh,)(IR)]+BF4(4; R = CH3 (a), CH2CH3(b), CH2CH2CH3(c), CH2Si(CH3), (d)) as analytically pure powders in 67-87% yields., The structures of 4a-d followed from their spectroscopic properties and in particular from the downfield shifts exhibited by the ICH carbons and protons in I3C and 'H N M R spectra., Oxidative addition show products such as [(q5-C,H,)Re(NO)(PPh,)(CH,)(Br)]+Xupfield ReCH 'H and 13CN M R resonances that are also strongly coupled to phosphorus.6 Crystals of the solvate 4d-(CH2Cl,),,, were grown from CH,Cl,/hexanes, and the X-ray structure was determined (Figure 1 ) as described in the Supplementary Material. The carbon-iodine bond (2.18 (1) %.) is very slightly longer than that in ethyl iodide (2.139 ( 5 ) A),' and the Re-I bond (2.678 (1) %.)is shorter than
(1) (a) Crabtree, R. H.; Faller, J . W.; Mellea, M. F.; Quirk, J. M. Organometallics 1982,1 , 1361. (b) Burk, M. J.; Segmuller, B.; Crabtree, R. H . Ibid. 1987,6, 2241. (2) For chelating aryl halide complexes o-C,H,X(DL,) (DL, = PAr,, S, Br, I), see ref 1 and the following: (a) Burk, M. J.; Crabtree, R. H.; Holt, E. M. Organometallics 1984,3, 638. (b) Crabtree, R. H.; Mellea, M. F.; Quirk, J. M. J . Am. Chem. SOC.1984,106, 2913. ( c ) Barcelb, F.; Lahuerta, P.; Ubeda, M. A,; Fcces-Foces, C.; Cano, F. H.; Martinez-Ripoll, M. J . Chem. Soc., Chem. Commun. 1985,43. (d) Solans, X.; Font-Altaba, M.; Aguilb, M.; Miravitlles, C.; Besteiro, J. C.; Lahuerta, P. Acta. Crystallogr., Sect. C: Cryst. Struct. Commun. 1985,C41, 841. (e) Cotton, F. A,; Lahuerta, P.; Sanau, M.; Schwotzer, W.; Solana, I. Inorg. Chem. 1986,25, 3526. (f') Kulawiec, R. J.; Holt, E. M.; Lavin, M.; Crabtree, R. H. Ibid. 1987,26, 2559. (9) Catala, R. M.; Cruz-Garritz, D.; Hills, A,; Hughes, D. L.; Richards, R. L.; Sosa, P.; Torrens, H . J . Chem. SOC.,Chem. Commun. 1987,261. (3) (a) A diene-chelated cyclopropyl bromide complex has recently been reported: Liotta, F. J., Jr.; Van Duyne, G.; Carpenter, B. K. Organometallics 1987,6 , 1010. (b) See, also: Cotton, F. A,; Ilsley, W. H.; Kaim, W. J . Am. Chem. SOC.1980, 102, 3475.
(4j (a) Fernlndez, J. M.; Gladysz, J. A. Inorg. Chem. 1986,25,2672. (b) Fernandez, J. M., unpublished results. (5) All new compounds were characterized by microanalysis, IR, and N M R ('H, 13C,"P) as described in the Supplementary Material. Selected N M R data (CD,CI,) for 4b,10b (-60 "C), and llb (-40 "C): IH N M R (6) 5.62, 5.56, 5.59 (s, C,H,), 3.77, 4.18, 4.43 (dq, J = 9, 7 Hz, C H " ) , 3.46, 3.73, 3.92 (dq, J = 9, 7 Hz, CHH'), 1.65, 1.62, 1.54 (t, J = 7 Hz, CH,); I3C N M R (ppm) 92.1, 91.9, 91.5 (s, C,H,), 24.0, 56.7, 69.9 (d, J = 3.1, 12.0, 1.8 Hz, CH2), 18.8, 17.8, 17.5 (s, CHI); 31P(ppm) 11.8, 12.9, 13.6 (s); NMR of ICH2CH3(CD,CI,) 'H N M R (a) 3.20 (q, J = 7.5 Hz, CHI), 1.82 (t, J = 7.5 Hz, CH,); "C N M R (ppm) 20.89 (s, CH,), -0.23 (s, CH,). (6) O'Connor, E. J., unpublished results, University of Utah; 192nd National Meeting of the American Chemical Society, Anaheim, CA, September 12, 1986; abstract INOR 347. (7) Kasuya, T.; Oka, T. J . Phys. SOC.Jpn. 1960, 15, 296. For other CCH,-l bond lengths (2.13-2.14 A), see: Williams, J. Q.; Gordy, W. J . Chem. Phys. 1950,18, 994; Ghisalberti, E. L.; Jefferies, P. R.; Raston, C. L.; Skelton, B. W.; Stuart, A. D.; White, A. H . J . Chem. Soc., Perkin Trans. 2 1981,583.
(30) (a) Pichler, H.; Schultz, H . Chem. Ing. Tech. 1970,12, 1160-1 174. (b) Masters, C. Adu. Organomet. Chem. 1979,17, 61-103. (31) A similar C - 0 bond breakage has been observed in the conversion of Cp*,TaH(q2-CH20) (Cp* = q5-C5Me5)to Cp*2Ta=O(CH,), including evidence for a preequilibrium involving Cp*,Ta(OCH,). See: van Asselt, A,; Burger, B. J.; Gibson, V. C.; Bercaw, J. E. J . Am. Chem. Sot. 1986,108, 5347-5349. (32) In view of ref 31, the conversion of 3 to 4 may proceed via the following: ( I ) reductive elimination to form a p-OCH,; (2) oxidative addition of the 0-CH, bond, generating a Ta-CH,: (3) Me transfer to p-CHO concomitant with deoxygenation. (33) Nijs, H. H.; Jacobs, P. A. J . Catal. 1980,66, 401-411. (34) Anton, A. B.; Parmeter, J. E.; Weinberg, W. H. J . Am. Chem. SOC. 1986,108, 1823-1833.
A General Class of Stable Alkyl Halide Complexes: Synthesis, Structure, and Reactivity of Alkyl Iodide Complexes of the Formula
[($-C5H5)Re(NO)(PPh3)(IR)]+BF4Charles H . Winter, Atta M . Arif, and J. A. Gladysz* Department of Chemistry, University of Utah S a l t Lake City, Utah 841 12 Received August 3, 1987
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J . Am. Chem. SOC.1987, 109, 7561-7563
halide complexes 5 and 6 also formed. Product identities were confirmed by GLC and N M R comparison to authentic samples. The synthesis of other alkyl halide complexes has been briefly explored. Analogous reactions of 1, HBF,.Et,O, and ethyl bromide or ethyl chloride gave ethyl halide complexes [($-CjHj)Re(NO)(PPh,)(XCH,CH,)]+BF,(lob, X = Br; l l b , X = Cl). This structural assignment was made on the basis of 'H, I3C,and 31P N M R spectra that closely match those of 4b. Complexes 10b and l l b decompose between -20 and 0 "C. Analogous pentamethylcyclopentadienyl complexes also can be prepared and will be described in a later publication. In summary, a variety of alkyl halide complexes are now readily accessible and can be expected to exhibit a rich and useful coordination chemistry.
Scheme 1. Synthesis and Reactions of Alkyl Iodide Complexes
CH,
de ON'
I
PPh,
_C" +
\PPh,
-R 1
de ON/
1
Re
+
\PPh3
- Ph3PR' BF,
(8)
IR
NCCH,
a b c d
7561
ON/
1
Acknowledgment. W e thank the N S F for support of this research and the N I H for a postdoctoral fellowship (C.H.W.).
'PPh,
I
R = CH, (67%) R = CH2CH3 (70%) R = CH,CH,CH, (87%) R = CHzSiiCH3), (81%\
those in (CO)4Re(p-I)2Re(CO)4and a related terminal iodide complex (2.81-2.83 A).* However, the structure is not appreciably distorted along an oxidative addition reaction coordinate, as the I-Re-P and I-Re-N bond angles (91.1-97.0') are close to idealized octahedral values (90'). Bond angles in iodonium salts RR'I'X- are typically ca. 95O, and a short I+/X- "secondary bond" (2.5-3.5 A) is usually found.9 In contrast, the Re-I-Cl bond angle in 4d.(CH2C1,), is 102.5 (5)', and the BF4- fluorine atoms are 1 4 . 0 0 8, from the iodine. Finally, the P-Re-I-C1 torsion angle is 169O, which places the alkyl substituent in the region between the small N O and medium cyclopentadienyl ligands. Thermal and chemical reactions of 4a-c have been briefly studied. First, 4a-c decompose over the course of 48 h in CD2C12 a t 25 "C to give primarily the bridging halide complexes (SS,R R ) -[ ( 0 5 - C , H 5 ) R e ( N O ) ( PPh,)(pX)(PPh,)(NO)Re($C5H5)]+BF4-( 5 , X = Cl,4 28-43%; 6,X = I, 46-61%; assayed by 'H and "P N M R with Ph3SiCH3 standard). The structure of new compound 6 was confirmed by an independent synthesis from iodide complex (q5-C,Hj)Re(NO)(PPh,)(I) (7)'O and Ag+BF,-." The mechanisms of formation of 5 and 6 are under investigation. Reactions of 4a-c with PPh, (1.2 equiv, 0.04 M in CDCI,, 25 OC, assayed as above) were complete within 15 min (Scheme I). Alkylation products Ph3PR'BF,- (8, 93-86%) and iodide complex 7 (>99-95%) formed. Product identities were confirmed by IH and 3'P N M R comparison to independently prepared authentic samples (Supplementary Material). Importantly, reactions of CH,I, CH3CH21,and CH3CH2CH21with PPh, under identical conditions were 70% complete after 4 h, and 510% and
