Organometallics 1986,5, 393-394
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plicated the interconversion. Now that this phenomenon is understood, it is evident that it provides the basis for an exceptionally simple synthesis of tetraorganylborates, as well as the basis for achieving a very simple conversion of organoboranes into Grignard reagents (eq 10). R3B + 3R'MgX 3RMgX + R'3B (10)
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Acknowledgment. We wish to thank the National Science Foundation (Grant CHE-8414171) for financial support of this research.
Stablllratlon of a Large Arsenlc-Oxygen Heterocycle vla Metal Coordlnatlon. The Synthesis and X-ray Crystal Structure of [Mo( CO),],[cyclo -(CH,AsO),] Arnold L. Rhelngold' and Anthony4 DlMalo Depafiment of Chemistty, University of Delaware Newark, Delaware 19716 Received November 5, 1985
Summary: I n the presence of molecular oxygen, Mo(C0)6,and cyc/o-(CH,As), form the first example of a metal-coordinated alkylarsaoxane, [Mo(CO),] [cyclo (CH,AsO),] (l), containing a 12-membered alternating As-0 ring coordinated to two Mo(CO), groups. The As-0 ring exists as a flattened, trans bimetal-capped cuboctahedron with two planes of three arsenic atoms positioned for coordination and a central plane of six oxygen atoms. Crystals of 1 are orthorhombic of space group Cmca, with a = 13.424 (2), A, b = 16.909 (3) A, c = 11.818 (2) A, Z = 4, and V = 2682.6 (7) A3.
Figure 1. Thermal ellipsoid diagram for ((CH,AsO),[Mo(CO),],I (1)and atom labeling scheme with hydrogen atoms deleted. Bond distances (A): Mo-As(l),2.556 (1);Mo-As(lb), 2.557 (1);MoAs(2), 2.535 (1);As(1)-0(3),1.793 (2); As(1)-0(4), 1.794 (3); As(2)-0(4a), 1.787(3). Bond angles (deg): As(l)-Mo-As(2), 92.8 (0); As(1)Mo-As(lb), 93.7 (0);As(a)-Mo-As(lb), 92.8 (0); Mo-h(1)-0(3), 116.9 (1); Mo-As(l)-0(4), 116.4 (1); Mo-As(2)-0(4a), 118.4 (1); Mo-As(2)-0(4c), 118.4; As(l)-O(B)-As(la), 119.7 (2); As(l)-O(4)-As(2a), 118.1 (2); 0(3)-&(1)-0(4), 100.9 (1);0(4a)-As(2)-0(4c), 101.2 (2).
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Alkylarsaoxanes, (RAsO),, are thought to exist as cyclotrimers, cyclotetramers, and other more highly associated, interchangeable ring and chain forms,l but none of the proposed structures has been isolated or confirmed ~rystallographically.~f The potential for arsaoxanes to serve as multidentate ligands offers a means for the iso// A lation of discrete species. We now report the synthesis and characterization of a dimolybdenumhexacarbonyl complex of cy~lo-(CH,AsO)~ containing a 12-membered As-0 Figure 2. A projection of the structure of 1 viewed down the heterocycle bridging Mo(CO), groups, ([M~(CO)~]~[cyclo- Mo-Mo' vector. (CH&O)6ll (1). Complex 1 is prepared from toluene solutions of Mo(C1 was separated from the much less soluble 2 in boiling O), and cyclo-(AsCH,), in which various quantities of CH2C12. The product ratio of 1 to 2 varies with the initial dioxygen are dissolved and heated in Carius tubes at 150 oxygen concentration; at the extremes, only 1 is isolated "C for 48 h. Upon slow cooling, pale yellow crystals of l4 in 77% yield (based on (CH3As),) with addition of stoialong with [MO(CO)~]~[~~C~O-(A~CH~)~~] (2)5 are obtained. chiometric quantities of O2 (eq 1)while only 2 is isolated in rigorously degassed systems (eq 2). (1)Durand, M.; Laurent, J.-P. J. Organomet. Chem. 1974,77, 225. Marsmann, H. C.; Van Wazer, J. R. J. Am. Chem. SOC. 1970,92,3969. (2)The literature abounds with names for compounds of formula RAsO: alkylarsaoxane, arsenosoalkane, alkylamine oxide, and alkylarsenious oxide are the most commonly encountered. (3)Arsaoxanes are among the oldest known organometallic compounds. [(CH3),AsOAs(CH3),]: Cadet de Gassincourt, L. C. Mem. Math. Phys. Saoants Etrangers. 1760,3,363.CH,AsO: von Baeyer, A. Justus Liebigs Ann. Chem. 1858,107,279. (4)(1) 'H NMR (CDCl,): 6 1.91;IR YCO 1980 s, 1906 s, 1875 m; decamp. temp, 300 "C. Anal. Calcd C, 14.47;H, 1.81;As, 45.16. Found: C, 14.48;H, 1.88;As, 45.36. (5)(2)'H NMR (benzene-&): 6 1.61 sh, 1.57s; IR vco 1926 8,1868m, 1843 m;decomp temp, 255 OC. Anal. Calcd: C, 15.25;H, 2.38. Found C, 15.27;H, 2.59.
0276-7333/86/2305-0393$01.50/0
{ [MO(CO)~I~(CH~AS)~O) (2)
2
Compound 1 crystallizes as discrete molecules (Figures 1and 2) without significant intermolecular contacts.6 The 0 1986 American Chemical Society
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Organometallics 1986, 5, 394-397
crystallographic site symmetry is 2/m; O(3) and O(3b) define the two fold rotational axis and 0(2), C(2), Mo, As(2), and C(4) define the mirror plane. The structure of 1 contains a 12-membered ring of alternating CH,As groups and oxygen atoms; these 12 atoms form a flattened cuboctahedron which is trans bicapped by Mo(CO), groups. The As-0 ring configuration and the crystallographic symmetry require a coplanar arrangement for the six oxygen atoms which is sandwiched between two planes of three As atoms each. These exterior planes or arsenic atoms are positioned to form fuc-Mo(CO),L, coordination environments at the metal center. The average of the three Mo-As distances, 2.55(1) A, compares closely to those found in known structure^.^ The average As-0 distance, 1.791 (3) A, is very similar to that found in other caged As(II1)-0 structures: As406(3), 1.80 A;8 As404(CHJ2(41, (av) 1.795(7);9and As303[(CH2),CCH3]( 5 ) (av) 1.77 (1) A.lo The As-Mc-As angles are slightly obtuse, (av) 93.1°, and consistent with octahedral Mo geometry, while the C-Mo-C angles are slightly acute, (av) 87.2 (3)O. Whereas the 0-As-0 angles, (av) 101.0 (l)', are very similar to As406,looo,to 3,101.8 ( 4 ) O , and to 5,100.5', the As-O-As angles in 1, 118.1 (2) and 119.7 (2)O, are considerably smaller than in 3,4, or 5, which are in the range 126-129'. This decrease in the As-0-As angles has the effect of flattening the cubooctahedron and better positioning the six As atoms for metal coordination. Complex 1 is electron precise with a clearly definable 18e count a t each metal center; each As(II1) atom serves as a conventional 2e donor. Our results suggest that the formation and stability of the cyclo-hexaarsaoxane ligand requires the presence of a stabilizing superstructure. The homoatomic cyclopentaarsine precursor to 1 reacts vigorously with dioxygen to form species of empirical formula CH,AsO, but the route to 1 undoubtedly involves considerable metal-centered assistance in the organization of a 12-membered ring. Ellermann et al." have recently reported a novel cryptand (6) containing an eight-membered [N(CH2CH2)3]8(As404)6 alternating As-0 ring in which each As atom is joined to two other A S 4 0 4 rings via N(CH2CH2-)3 tripod bridge networks. The As-0 bond distance (average 1.79 (5) A and the As-O-As (average 118 ( 2 ) O ) and 0-As-0 (average 101 ( 1 ) O ) angles compare closely to those found in 1. To date the known structures containing organoarsaoxane ring systems are either caged by organic linkages, 4-6, or by metal carbonyl coordination, 1, suggesting that such rings may prove to be very difficult to isolate without a superstructure. In fact, NMR studies' clearly indicate the cyclotrimers and tetramers of (CH3AsO), are involved in dynamic reorganization equilibria with higher cyclic and possibly linear species. A complete discussion of the homocyclic decaarsine (6) Crystal data for 1, C,,H,& MozO,z: M,= 995.7, orthorhombic, space group Cmca; a = 13.424 (2) b = 16.909 (3) A, c = 11.818 (2) A, V = 2682.6 (7) A, 2 = 4, Deded= 2.47 g ~ m - F(000) ~, = 1872, ~ ( M Ka) o = 80.6 cm-'. A pale yellow crystal (0.33 X 0.34 X 0.35 mm) was grown from CH,Cl,. Data were collected at 23 "C on a Nicolet R3 diffractometer. The structure was solved by direct methods and difference Fourier techniques. The 1605 symmetry-allowed reflections collected (+h, +k, +l; 4O 5 26' 5 50°) were corrected for absorption; of these, 1309 with F, t 4u(F,) were used in refinement with anisotropic parameters for all non-hydrogen atoms. Hydrogen atom contributions were idealized and updated. A t convergence R p = 2.68%, RWVF = 2.94%, and GOF = 1.337 with a 13.4 data to parameter ratio. (7) Rheingold, A. L.; Foley, M. J.; Sullivan, P. J. J. Am. Chem. SOC. 1982, 104, 4727. (8) Bozorth, R. M. J. Am. Chem. SOC.1923,45, 1621. (9) Kopf, J.; Von Denten, K.; Klar, G. Inorg. Chim.Acta 1980,37,67. (10) Mckerley, B. J.; Reinhardt, K.; Mills, J. L.; Reisner, G. M.; Korp, J. D.; Bernal, I. Inorg. Chim. Acta 1978, 31, L411. (11)Ellermann, J.; Veit, A.: Lindner, E.; Hoehne, S. J. 0r.wnomet. Chem. 1983.252, 153.
1,
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complex 2 will appear elsewhere.12 Acknowledgment. The National Science Foundation provided assistance in the purchase of the diffractometer. The Center for Catalytic Science and Technology at the University of Delaware provided support for the research. Registry No. 1,99686-49-4; 2,99686-50-7;MO(CO)~, 1393906-5; cyclo-(AsCHB)B, 20550-47-4.
Supplementary Material Available: Tables of atomic coordinates, a complete listing of bond distances and angles, anisotropic temperature factors, hydrogen atom coordinates, and observed and calculated structure factors (13 pages). Ordering information is given on any current masthead page. (12) Rheingold, A. L.; DiMaio, A.-J.; Fountain, M. E., manuscript in preparation.
Stepwise Assembly of a Trinuclear Bis(carbyne) Complex from Cyclopentadlenylcobalt Units and Bls(trlmethyls1lyl)acetylene: Isolation and Conversion of Cp2M2(RC=CR)and (CpM),( RC=CR) [M = Co and R = (CH,),SI] Bruce Eaton, Joseph M. O'Connor, and K. Peter C. Vollhardt Department of Chemistry University of California at Berkeley and the Materials and Molecular Research Division Lawrence Berkeley Laboratory Berkeley, California 94 720 Received August 26, 1985
Summary: Reaction of (q5-C,H5)Co(C2H& (7) with bis(trimethy1silyl)acetylene(btmsa) in THF at 23 OC gives (~5-C,H,)2Co,(btmsa) (9). The structure of 9 was determined by X-ray crystallography, revealing the presence of a Co-Co double bond: 2.18 A, to our knowledge the shortest cobalt-cobalt bond in existence. Complex 9 reacts further with 7 at 55 OC to produce ($-C,H,),Co,(btmsa) (10). Complex 10 adds carbon monoxide to give ($'-C,H,),Co,(btmsa)(CO) (11). Both 10 and 11 are converted to (T~-C,H~)~CO~[~,-~'-CSI(CH,),] (6) in boiling m -xylene or hot methylcyclohexane. A crossover experiment involving (~5-CH,C,H,),Co2(btmsa) and 10 establishes the intramolecular nature of the rearrangement to 6.
Mononuclear transition-metal complexs of the cobalt triad 1 react with alkynes to give trinuclear bis(carbyne) clusters 2 (Scheme I).1-3 Among the alkyne substrates which have been examined in these reactions, bis(trimethylsily1)acetylene(btmsa) exhibits anomalous behavior. Sakurai and Hayashi have reported that 1 (M = Co) converts to 3 in 93% yield in the presence of 2 equiv of btmsa in boiling ~ y l e n e . ~ More recently, we reported that 1 (M (1) (a) Fritch, J. R.; Vollhardt, K. P. C.; Thompson, M. R.; Day, V. W. J . Am. Chem. SOC. 1979,101,2768. (b) Fritch, J. R.; Vollhardt, K. P. C. Angeru. Chem.,Int. Ed. Engl. 1980,19,559. (c) Fritch, J. R.; Vollhardt, K. P. C. Isr. J . Chem., in press and the references therein. (2) Yamazaki, H.;Wakatsuki, Y.; Aoki, K. Chem. Lett. 1979, 1041. (3) Gardner, S. A.; Andrews, P. S.; Rausch, M. D. Inorg. Chem. 1973, 12,2396. Toan, T.; Broach, R. W.; Gardner, S. A.; Rausch, M. D.; Dahl, L. F. Inorg. Chem. 1977, 16, 279. (4) Sakurai, H.; Hayashi, J. J. Organomet. Chem. 1972,39,365; 1974, 70, 85.
0 1986 American Chemical Society
