C O M M U N I C A T I O N S
Figure 2. Views (left to right) of the molecular structures of the complex cations of 6[PF6-], 7[BArF -], and neutral 9 (H-atoms omitted for clarity).
4
with Pd have been characterized by Carmona,13 and Spencer has
reported the structure of [(dtbpe)Ni(CH2CH3)][BF4] to have a
â-C-H agostic interaction involving Ni and the ethyl ligand.11c
References
(1) (a) Jolly, P. W.; Wilke, G. The Organic Chemistry of Nickel; Academic
Press: New York, 1974. (b) Hegedus, L. S. Coord. Chem. ReV. 2000,
204, 199-307.
Cations 5-7 are highly fluxional on the NMR time scale. Even
at -90 °C (CD2Cl2), all nine CH3 protons of the neopentyl ligand
of 5 appear equivalent (singlet), suggesting that the γ-agostic
interaction is weak and the rotation of the tert-Bu group rapid.14
The barrier to a higher-energy dynamic process that equates the
PtBu2 substituents of the dtbpe ligand (e.g., the windshield-wiper
movement of the alkyl group across the pseudo C2-axis) has been
determined for 5 and 7 by VT NMR methods and is ∼13.0 kcal/
mol for both complexes.15
Reaction of 5-7 with NaN(TMS)2 results in deprotonation of a
γ-CH3 group to give the metallacyclobutane complexes 8-10
(Scheme 1) as yellow crystalline solids in good yields. The solid-
state structure of 9 (Figure 2) features square-planar Ni(II) and a
puckered (138.6°) metallacyclobutane moiety. NMR data indicate
analogous structures for 8 and 10. Whitesides has reported that
related Pt metallacyclobutanes, (PR3)2Pt(CH2CMe2CH2) (R ) Cy,
iPr), undergo reductive elimination to give 1,1-dimethylcyclopro-
pane.16 While solutions of 9 are stable at 140 °C with respect to
cyclopropane elimination, benzene solutions of 8 and 10 quanti-
tatively eliminate the cyclopropanes 11 and 12 at ambient temper-
ature, as determined by NMR and GS-MS analysis, with formation
of [(dtbpe)Ni]2(C6D6) (eq 2).10,17
(2) (a) Tolman, C. A.; McKinley, R. J.; Seidel, W. C.; Druliner, J. D.; Stevens,
W. R. AdV. Catal. 1985, 33, 1-46. (b) Seidel, W. C.; Tolman, C. A.
Ann. N. Y. Acad. Sci. 1983, 415, 201-221.
(3) (a) Keim, W. Angew. Chem., Int. Ed. Engl. 1990, 29, 235-244. (b) Vogt,
D. In Aqueous-Phase Organometallic Catalysis; Cornils, B., Akerrmann,
W., Eds.; Wiley-VCH: Weinheim, 1998; pp 541-547.
(4) (a) Wilke, G. Angew. Chem., Int. Ed. Engl. 1988, 27, 185-206. (b) Green,
M. L. H.; Munakata, H. J. Chem. Soc., Dalton Trans. 1974, 269-272.
(5) (a) Mulrooney, S. B.; Hausinger, R. P. FEMS Microbiol. ReV. 2003, 27,
239-261. (b) Svetlitchnyi, V.; Dobbek, H.; Meyer-Klaucke, W.; Meins,
T.; Thiele, B.; Romer, P.; Huber, R.; Meyer, O. Proc. Natl. Acad. Sci.
U.S.A. 2004, 101, 446-451. (c) Dobbek, H.; Svetlitchnyi, V.; Gremer,
L.; Huber, R.; Meyer, O. Science 2001, 293, 1281-1285. (d) Drennan,
C. L.; Heo, J.; Sintchack, M. D.; Schreiter, E.; Ludden, P. W. Proc. Natl.
Acad. Sci. U.S.A. 2001, 98, 11973-11978. (e) Hausinger, R. P. Nat. Struct.
Biol. 2003, 10, 234-236. (f) Webster, C. E.; Darensbourg, M. Y.; Lindahl,
P. A.; Hall, M. B. J. Am. Chem. Soc. 2004, 126, 3410-3411. (g) Volbeda,
A.; Fontecilla-Camps, J. C. J. Chem. Soc., Dalton Trans. 2003, 4030-
4038. (h) Ermler, U.; Grabarse, W.; Shima, S.; Goubeaud, M.; Thauer,
R. K. Science 1997, 278, 1457-1462. (i) Craft, J. L.; Horng, Y.-C.,
Ragsdale, S. W.; Brunold, T. C. J. Am. Chem. Soc. 2004, 126, 4068-
4069.
(6) (a) Uhlig, E.; Walther, H. Z. Chem. 1971, 11, 23-24. (b) Uhlig, E.;
Walther, H. Z. Anorg. Allg. Chem. 1974, 409, 89-96. (c) Overbosch, P.;
van Koten, G.; Spek, A. L.; Roelofsen, G.; Duisenberg, A. J. M. Inorg.
Chem. 1982, 21, 3908-3913. (d) Barefield, E. K.; Krost, D. A.; Edwards,
D. S.; Van Derveer, D. G.; Trytko, R. L.; O’Rear, S. P. J. Am. Chem.
Soc. 1981, 103, 6219-6222.
(7) Eaborn, C.; Hill, M. S.; Hitchcock, P. B.; Smith, D. J. J. Chem. Soc.,
Chem. Commun. 2000, 691-692.
(8) Mindiola, D. J.; Waterman, R.; Jenkins, D. M.; Hillhouse, G. L. Inorg.
Chim. Acta 2003, 345, 299-308.
(9) (a) Mindiola, D. J.; Hillhouse, G. L. J. Am. Chem. Soc. 2001, 123, 4623-
4624. (b) Melenkivitz, R.; Mindiola, D. J.; Hillhouse, G. L. J. Am. Chem.
Soc. 2002, 124, 3846-3847.
(10) See Supporting Information for complete experimental, spectroscopic, and
crystallographic details.
In summary, we have prepared several three-coordinate, mon-
omeric Ni(I) alkyl complexes (2-4). While thermally robust, they
undergo mild one-electron oxidation to give the corresponding Ni-
(II) complex cations (5-7). In contrast to cationic amido and
phosphido analogues that undergo R-deprotonation to afford imido
and phosphinidene derivatives, deprotonation of 5-7 occurs at a
γ-CH3 group to give metallacyclobutane products (8-10), not
(dtbpe)NidCHR. Reactivity studies of these unusual complexes are
underway.
(11) (a) Jolly, P. W.; ComprehensiVe Organometallic Chemistry; Pergamon:
Oxford, 1982; Vol. 6, pp 37-100. (b) Bochmann, M.; Hawkins, I.;
Hursthouse, M. B.; Short, R. L. J. Chem. Soc., Dalton Trans. 1990, 4,
1213-1219. (c) Conroy-Lewis, F. M.; Mole. L.; Redhouse, A. D.; Litster,
S. A.; Spencer, J. L. J. Chem. Soc., Chem. Commun. 1991, 1601-1603.
(12) The 2 Ni-C distances in 6[PF6-] represent a disordered average of the
Ni-CH2- and γ-CH3 group. We did not attempt to model this disorder.
t
The structure of 5[PF6-] displayed conformational disorder of the Bu
groups of the dtbpe ligand and the CH3 groups of the neopentyl ligand,
resulting in a poor-quality structure.
(13) (a) Campora, J.; Gutierrez-Puebla, E.; Lopez, J. A.; Monge, A.; Palma,
P.; del Rio, D.; Carmona, E. Angew. Chem., Int. Ed. 2001, 40, 3641-
3644. (b) Campora, J.; Lopez, J. A.; Palma, P.; Valerga, P.; Spillner, E.;
Carmona, E. Angew. Chem., Int. Ed. 1999, 38, 147-151.
(14) Similar γ-agostic neopentyl interaction in a Rh(I) complex has been
reported. Urtel, H.; Meier, C.; Eisentrager, F.; Rominger, F.; Joschek, J.
P.; Hofmann, P. Angew. Chem., Int. Ed. 2001, 40, 781-784.
(15) (a) Gutowsky, H. S.; Holm, C. H. J. Chem. Phys. 1956, 25, 1228-1234.
(b) Kurland, R. J.; Rubin, M. B.; Wise, W. B. J. Chem. Phys. 1964, 40,
2426-2431.
Acknowledgment. G.L.H. thanks the National Science Founda-
tion for financial support (CHE-0244239). D.J.M. acknowledges
postdoctoral fellowship support from the Ford Foundation and the
NIH. ESR acquisition and simulation assistance from Prof. Karsten
Meyer, Cora MacBeth, David Jenkins, and Rory Waterman is
appreciated.
(16) DiCosimo, R.; Whitesides, G. M. J. Am. Chem. Soc. 1982, 104, 3601-
3607.
(17) Bach, I.; Porschke, K.-R.; Goddard, R.; Kopiske, C.; Kruger, C.; Rufinska,
A.; Seevogel, K. Organometallics 1996, 15, 4959-4966.
Supporting Information Available: Experimental and spectro-
scopic details (PDF, CIF). This material is available free of charge via
JA047052Z
9
J. AM. CHEM. SOC. VOL. 126, NO. 34, 2004 10555