ORGANOMETALLICS Volume 2 , Number 4 , April 1983
0 Copyright 1983 American Chemlcal Sociew
Studies of Organomoiybdenum Compounds. 2. Synthesis, Structure, and Properties of Dioxodineopentyi(2,2'-bipyridyi)molybdenum(VI) and of Related Compounds Gerhard N. Schrauter,* Laura A. Hughes, and Norman Strampach Department of Chemlstty, University of Callfornle at San Diego, La Job, Cailforn& 92003
Fred Ross, Dawn Ross, and Elmer 0. Schlemper" Department of Chemistty, Unlversitv of Missouri, Columbia, Mlssouri 6521 I Recelved August 30, 1082
The synthesis of M o ( O ) ~ [ C H ~ C ( C H , ) & by ( ~ ~the ~ ) reaction of M ~ ( O ) ~ ( B r ) ~ ( bwith p y ) neopentylmagnesium bromide is described. This new dialkyl derivative of dioxomolybdenum(V1) is stable to air up to 182 OC. Thermolysis at higher temperatures is initiated by M o C bond homolysis and H abstraction to yield neopentane as the major gas-phase hydrocarbon product. The high thermal stability is primarily due to the absence of hydrogen in @-positionrelative to molybdenum; higher n-alkyl derivatives of this class of compounds decompose spontaneously by @ elimination and cannot be isolated. Decomposition of the dineopentyl complex is slow in neutral protic solvents but occurs on heating in strong alkali, in mineral acids, and with particular ease under reducing conditions. The complex M O ( O ) ~ [ C H ~ C ( C H(bpy) ~)~] crystallizes from diethyl ether in the monoclinic space group C2IC,with a = 24.309 A, b = 12.635 c = 16.542A, and @ = 107.68O,with 2 = 8. The three-dimensional X-ray data were measured with the 6-26 scan technique; the structure was resolved by Patterson and Fourier methods. The M ~ ( O ) ~ ( b pmoiety y) is essentially coplanar, the independent Mo-N and Mo-0 distances are nearly the same, and the Mo-C bond lengths of 2.236 (5)A are 0.04 A longer than in the previously reported dimethyl derivative. Both C(CH& groups of the two neopentyl residues are positioned above and below the MO(O)~ group. Two of the CH3groups of each neopentyl residue are staggered about one M d bond to minimize the repulsion between the methyl group protons and the oxygen atoms. Repulsive interactions between the oxygen atoms and the neopentyl methyl groups cause a widening of the Mo-C-C angle from normal tetrahedral to 118.9O and a narrowing of the C-Mo-C angle to 145.8', which is 3.2O smaller than in the dimethyl derivative.
x,
Introduction The reaction of ( b p y ) M ~ ( O ) ~ B(1) r ~ with methylmagnesium bromide has been shown recently' to yield the complex M 0 ( 0 ) ~ ( C H ~ ) ~ ( b(2). p y ) Its remarkable stability prompted us to extend our studies t o the synthesis of higher dialkyldioxomolybdenum(V1) complexes of this type. While such complexes could not be obtained for reasons to be discussed, we were successful in preparing the dineopentyl derivative M O ( O ) , [ C H , C ( C H J ~ ] ~ ((31, ~~~) whose properties and structure will be described in the following. The reaction of 1 with neopentylmagnesium bromide has previously been shown2 to yield the purple complex Mo-
R
-
R,
R2= Br
RI ' R2= CH3
(2)
RI = R2' CHz-C(CH3)3 (3) RI c C H ~ - C ( C H ~ ) ~ R p = Br
(1) Schrauzer, G. N.; Hughes, L. A.; Strampach, N.; Robinson, p.; Schlemper, E. 0. Organometallics 1982, I , 44. (2) Schrauzer, G. N Hughes, L. A.; Strampach, N. Z. Naturforsch. B: 1982, Anorg. Chem., Org. Chem. 37B, 380.
(1)
]
(4)
(O),[CH,C(CH,),](Br)(bpy)(4). The colorless alkaline hydrolysis product of 4, the anion (CH3)3CCH2M003-(5), has also been reporteda2 As other alkyl molybdates it is
0276-7333/83/2302-0481$01.50/0 0 1983 American Chemical Society
Schrauzer et al.
482 Organometallics, Vol. 2, No. 4, 1983 Table I. Summary of Phvsical Prowrties of ComDlexes 2 and 3 physical 2 3 property mp,"C a 230 dec 180 dec 934,905 922,890 IR 'MO=O cm-l 'H NMR,b ppm 6bpy 7.5-9.5 (8) 7.5-9.5 (8) (intensities) ~ C H , 1.15 (4) SCH, 0.58 (6) 0.95 (18) I
uv-vis hmax: nm (€1
345 (2000) 365 (1900) 303 (19 600) 304 (18 500) 292 (18 400) 293 (17 000) 283s (14 300) 283s (10 300) 250 (25 400) 245 (24 900) Chemical shifts are relative to Me$, a In KBr. measured in CDCl,, Measured in CH,Cl,. metastable, decomposing into MOO:- and C(CHJ4; in pH 11 buffered aqueous solution the t l l zis 282 min a t 70 "C and ca. 15 days a t 23 0C.2,3 The only other known neopentyl derivatives of oxomolybdate(VI)are the compounds Mo(O)[CH,C(CH,),I,(Cl) (6) and MdO) [CH2C(CW,I4 (7) described by Osborn and his scho01.~
Experimental Section Reagents and Chemicals. All reagents and chemicals obtained from commercial sources were of analytical or reagent grade purity and were used without further purification. Tetrahydrofuran (Mallinckrodt) was dried over potassium and distilled immediately prior to use. The argon was of 99.998% purity and was dried by passage over KOH pellets. Complex 1, Mo(0)2Br2(bpy),was prepared according to Hull and Stiddardas Synthesis of Mo(O)2[CHzC(CH3)3]z(bpy) (3). Neopentyl magnesium chloride was prepared in tetrahydrofuran according to standard methods, usually in batches from 0.5 g of Mg and 1.5 cm3of neopentyl chloride in 25 cm3of THF, resulting in an approximate 0.5 M solution. A stirred suspension of 2 g of 1 in 100 cm3 of dry THF was cooled to -10 OC by means of a dry ice/acetone/water bath. Under an atmosphere of argon, 20 cm3 of a 0.5 M solution of neopentylmagnesium chloride was added dropwise. After 2 h of reaction at -10 "C, the solution was allowed to warm to room temperature and 400 cm3 of water was added to the reaction solution. The product was extracted into CH2C12. Upon evaporation of the dried solvent, bright yellow crystals precipitated. These were collected by vacuum filtration and dried: mp 182 "C dec; yield, 459'0, based on 1. Anal. Calcd for C&&10N202: C, 56.33; H, 7.09; Mo, 22.50; N, 6.57; 0,7.50; mol. wt. 426.40. Found C, 56.55; H, 7.60; Mo, 22.62; N, 6.50; 0, 6.73; mol. wt. 430 (cryoscopic in benzene). Physical Properties. Fourier transform 'H N M R spectra were obtained for a solution of 3 in CDC13 by using a Varian HR22O/Nicolet T" 100 spectrometer. Chemical shifts and intensities of the observed signals of 3 are given in Table I together with the frequencies of important bands in the IR spectra. Chemical Properties. Thermolysis. Thermolyses of complexes 2 and 3 were performed in argon-filled, serum-capped, Pyrex test tubes of 10-cm length and 11-mm diameter. The tubes were heated to 300 "C for a measured time, typically for 30 s, and gas samples (0.5 cm3)for hydrocarbon analyses by GLPC were withdrawn. A Hewlett-Packard Model 700 gas chromatograph fitted with an 8 ft X in. column packed with phenyl isocyanate on Porasil C operating at 50 OC with an FID detector was used for hydrocarbon detection. The gas phase was also analyzed for H, by GLPC using a column of 6 f t X in., filled with molecular sieves (5 A), operating at 27 "C, and employing TC detection. (3) Schrauzer, G. N.; Hughes, L. A.; Strampach, N. Proceedings of the 4th International Conference on Chemistry and Uses of Molybdenum, Aug 9-13, 1982, in press. (4) Kress, J. R. M.; Russell, M. J. M.; Wesolek, M. G.; Osborn, J. A. J. Chem. Soc., Chem. Commun. 1980, 431. (5) Hull, C. G.; Stiddard, M. H. B. J. Chem. SOC.1966, 1633.
Table 11. Initial Hydrocarbon and Hydrogen Formation during the Thermolysis of Comdexes 2 and 3 at 300 "C for 30 s products 2 3 (% yield) a ba a ba 75.3 91.1 7.7 13.6 CH, 5.5 4.2 0.9 1.5 CZH, 1.1 1.6 C3H6 9.8 5.7 i-C,H, i-C4Hlo 1.1 3.4 neo-C, H,, 44.7 75.8 H, 17.7 3.5 35.8 In Thomas silicone bath oil.
Hydrocarbons were identifed by comparison of the retention times and coinjection of authentic samples of hydrocarbons as well as by mass spectrography, employing an LKB 9000 instrument. Results of thermolysis experiments are summarized in Table 11. Photolysis. Solutions of complexes 2 and 3 were exposed to visible and UV light in anhydrous CH30H as the solvent. Solutions of the complexes were placed into Pyrex or quartz test tubes fiied with argon. These were exposed to the light of either a 150-W GE flood light or a 360-W Hg-arc Hanovia UV lamp at a distance of about 12 cm. A stream of cold air was blown over the tubes to maintain the temperature at 50 OC. The gas phase was analyzed for hydrocarbons and H2 by GLPC as described above. After 2 h of exposure to UV light, 2 decomposed quantitatively to yield CHI. Photolysis of 3 under the same conditions was 15% complete and afforded mainly neopentane with traces of methane, ethane, isobutane, and isobutene in the gas phase. After 2 h of exposure of the complexes to the visible light source, 50% of the theoretical yield of CHI was observed from 2. Under the same conditions,solutions of 3 decomposed only to the extent of about 0.3%, affording neopentane as the only gas-phase hydrocarbon product. Solvolysis Experiments. Weighed amounts of complexes 2 or 3, usually 2-5 mg, were placed into glass bottles of 38-cm3 capacity. These were filled with argon and serum capped. Reactions were initiated by injecting a known volume (usually 5 cm3) of solvent or of the reactant solution. Gas samples were withdrawn at regular intervals and analyzed for hydrocarbons by GLPC as described above. Structure Analysis. Crystals suitable for X-ray crystallographic analysis were obtained by recrystallizing 3 from diethyl ether. This afforded crystals containing 0.5 molecules of diethyl ether of crystallization per molecule of complex. A crystal of approximate dimensions 0.08 X 10 X 0.30 mm was mounted on an Enraf-Nonius CAD-4 automated diffractometer for data collection. An outline of crystallographic and data collection parameters is given in Table III. The monoclinic (C2/c) unit-cell dimensions were determined by a least-squares fit of 25 reflections obtained by automatic centering on the diffractometer. Intensity data (294 K) were obtained by the 8-28 step scan technique using Mo Ka radiation (A = 0.7107 A). A total of 5141 reflections were measured out to 28 = 45". The intensities of three standard reflections measured after each 8000 s of X-ray exposure showed approximately 25% decrease during the data collection,and the data were corrected for this effect. Orientation was checked after every 200 reflections by recentering three reflections. If any of these were significantly off center, all 25 initial reflections were recentered, and a new orientation matrix was obtained. Several psi scans indicated that the transmission varied by less than 2% or so, thus no absorption correction was applied. Averaging of equivalent reflections yielded 2372 independent reflections with F, > 2(u(F0)); these were used to solve and refine the structure u2(Fo2)= u2countiag+ (0.05F,2)2and u(F,)= u(F,2)/2F0. The structure was solved by Patterson and Fourier methods. Least-squares refinement minimizing E w ( F , - Fc)2,where w = 1/u[FOl2, converged with R = EllFol - ~ F c ~ ~=/0.048 ~ F and o R, = [Ew(F,- F 3 2 / 1 w F 2 ] 1 /= 2 0.071. Hydrogen atoms were located by a combination of difference Fourier methods and chemical reasonability and were held near "ideal" X-ray positions.6 The (6) Churchill, M. R. Inorg. Chem. 1973, 12, 1213.
Organometallics, Vol. 2, No. 4, 1983 483
Organomolybdenum Compounds
Table 111. Crystallographic, Data Collection, and Refinement Parameters diffractometer 24.309 (20) A , A (MoKa) 12.635 (2) M , cm-' 16.542 (10) abs correctn not applied 107.68 (4) c2/c 1.272 (3) 8 variable, to maintain 3% counting scan speed 4841 (6) statistics to a max time of 90 s/
total no. of observns
5141
no. of indep reflctns 3174 no. of indep reflectns with Fo > 20(F0) 2372 used in structure refinement R(F0)
0.048
Rw(F0)
0.071
largest shift on the last cycle was 0.06 times the esd of that parameter, and the error of an observation of unit weight was 1.98. Atomic scattering factors were taken from ref 7 and anomalous scattering factors were included in F,. Final atomic positional parameters and thermal parameters are included in Table IV; F, and F, values are deposited in the microfii edition. Selected interatomic distances and angles are given in Tables V and VI.
Discussion $ynthesis of 3 and of Related Complexes. The products of the reaction of 1 with stoichiometric amounts of alkylmagnesium bromides are the purple monoalkyl derivatives 4, which have been described elsewhere. Substitution of the remaining bromide ion in 4 according to eq 1 occurs on the reaction with excess organoR
(1) -MgBrX +RMgX' R (bPY)40$ R
I
0
tRMgX
dr
0
-MpBri
(bpy)Mo:
I
STABLE R = CH,
CH2-C(CH3)3
:
UNSTABLE R = C 2 H 5 , higher
(1)
n-alkyl
magnesium reagent, but stable dialkyl complexes Mo(0)2R2(bpy)have thus far been obtained only with R = CH3 and, as is shown herein, with R = CH2C(CH,),. In the attempted synthesis of the diethyl derivative, the intermediate purple monoethyl bromide species reacted with a second molecule of the organomagnesium reagent. However, instead of the formation of an isolable diethyl derivative, a spontaneous decomposition reaction took place, accompanied by the evolution of a 1:l mixture of ethylene and ethane that could not be prevented by lowering the reaction temperature. Attempts to prepare a methyl ethyl complex, either by the reaction of Mo(O),(C2H5)(Br)(bpy)with CH3MgBr or in the reverse order of alkylation, likewise failed to produce isolable dialkylated species. Instead, the evolution of a 1:l mixture of ethylene and methane was observed. The higher di-n-alkyl species evidently are inherently unstable, undergoing spontaneous (7) 'International Tables for Cryetallography"; Kynoch Press: Birmingham, England, 1974;Vol. IV.
scan mode
e -2e (96 steps), 16 background
scan width, deg data limits, 213,
(0.50
each side and 64 peak + 0.35 tan 0 ) 2-49
deg
monochromation graphite monochromator largest shift/error 0.06 on last cycle decomposition by way of /3 elimination and reductive Mo-C bond cleavage in terms of eq 2. The dimethyl and C2H5
I
IM 0) 41 H +fH2 'CH2
+
+
-C2H4
( M d t CZHB
(2)
the dineopentyl derivatives 2 and 3 are obviously stable because the low-energy pathway of decomposition by way of /3 elimination is not available. Thermolysis. Although the thermal decomposition of 3 begins at 182 "C, it is slow at this temperature and hence was studied at 300 "C. The rate of thermolysis is relatively slow even a t 300 "C, however, and requires ca. 60 s for completion. Thermolysis is further complicated by secondary reactions involving the hydrocarbon thermolysis products, e.g., cracking, disproportionation, hydrogenation/dehydrogenation, carbide formation, etc. To obtain information on the initial decomposition reactions, the thermolyses at 300 "C were typically terminated after short (30 s) and long (2 min) reaction times. The hydrocarbon yields were in the order of 40-60% under all conditions investigated. Neopentane was identified as the first hydrocarbon product in the gas phase under all conditions chosen, but the yields only approach about 50% of theoretical. On continued heating, hydrogen, methane, isobutene, and isobutane appear in the gas phase. Homolysis of a Mo-C bond appears to be the initial event, which is followed by hydrogen abstraction and other reactions. When the thermolysis of 3 is conducted in a high-boiling solvent containing abstractable hydrogen atoms (e.g., silicone oil), neopentane becomes the nearly exclusive product and hydrogen is no longer formed (see Table 11). The neopentyl radicals generated on thermolysis in the absence of a solvent apparently abstract hydrogen atoms from neopentyl residues of neighboring molecules of 3, thus producing new organic radical species which terminate in part by fragmentation, hydrogen abstraction, or loss of hydrogen; hydridomolybdenum as well as (alky1idene)- and (alky1idyne)molybdenum species may be formed as intermediates. Since the formation of an alkylidyne complex, [ (CH,),CCM~(neopentyl)~]~, was ob-
484 Organometallics, Vol. 2, No. 4, 1983 Table IV. Weighed Least-Squares Planes and Final Positional Parameters for 3 atom X Y z dist, A Plane l a Atoms in Plane 2.2789 0.001 3.2609 -0.1116 3.0855 0.5028 0.0221 -0.012 0.016 5.2887 0.6127 1.4362 1.5942 -0.4699 2.2356 -0.037 0.6127 1.4362 0.016 5.2887 0.4197 -0.6502 1.9405 -0.019 1.8168 0.7597 -1.9577 -0.017 1.2070 -2.6358 2.9285 0.002 1.2964 -1.9807 4.1230 0.019 4.1993 0.9383 -0.6456 -0.015 5.4183 1.0043 0.1614 0.019 6.6392 1.4682 -0.3486 0.003 1.5314 0.5217 -0.039 7.7218 7.6109 1.1505 1.8162 -0.054 6.3800 0.6839 2.2379 -0.013 Other Atoms 4.1696 -1.8819 1.2573 2.139 3.3479 -3.2040 1.2355 3.193 2.8752 -3.5992 2.6105 3.087 3.034 2.1296 -3.0692 0.3072 4.2771 -4.2811 4.566 0.6712 2.1143 2.4331 -2.127 3.2435 2.0356 2.8286 3.0377 -3.236 0.8691 2.6880 2.1157 -3.127 2.3811 4.3080 3.1592 -4.573 1.7005 2.3145 4.3824 -3.191
1.5942 5.2887 4.1692 3.3479 4.2771 3.2435 2.0356 2.3811 3.2609 3.0855 3.9183
Plane z b Atoms in Plane -0.4699 2.2356 0.6127 1.4362 -1.8819 1.2573 -3.2040 1.2355 -4.2811 0.6712 2.1143 2.4331 2.8286 3.0377 4.3080 3.1592 Other Atoms -0.1116 2.2789 0.5028 0.0221 -0.4355 3.8211
Schrauzer et al. Table V. Selected Bond Distances ( A ) esd
0.001
0.005 0.005 0.005 0.005 0.007 0.008 0.009 0.007 0.006 0.006 0.007 0.007 0.008 0.007 0.006 0.007
-W)
-C(11) -C(16) -NU 1 -N(2) C(1)-C(2 1
a
1.709 (3) 1.706 (3) 2.237 (5) 2.235 (5) 2.348 (4) 2.317 (4) 1.354 (8) 1.376 (8) 1.369 1.377 1.386 1.392 1.356 1.379 1.374
C(l1)-C(12) C(16)-C(17) C(12)-C(13) C(12)-C(14) C(12)-C(15) C(17)-C(18) -C(19) -C(20)
1.546 (7 1.530 (7 1.507 (8 1.536 (8 1.522 (8 1.491 (8 1.526 (8 1.474 (8 1.512 1.336 1.369 1.347 1.346 1.350 1.467
Average value.
is required to afford quantitative yields of neopentane in terms of eq 3. Due to the hydrophobic nature of the
0.008
0.008 0.009 0.007 0.007 0.009 0.008 0.011
0.057 0.040 -0.028 -0.070 -0.025 -0.018 -0.104 0.008
0.004 0.005 0.007 0.007 0.011 0.007 0.007 0.009
-0.358 1.939 -2.053
0.001
0.005 0.005
x2 Values plane no.
Mo-O( 1)
XZ
1 205 2 561 Dihedral Angles between Planes 1 and 2: 90.8"
Plane 1: A , 0.2306; B, -0.9357; C, -0.2669; D, 0.2474. Plane 2: A , -0.2708; B, 0.2158; C, -0.9381; D, -2.6872.
served8 in the reaction of Mo(0)C14 with dineopentylmagnesium-dioxan, it is possible that related alkylidyne species are formed in the thermolysis of 3. In the thermolysis of 2 a t 300 "C, CHI is the main initial product. In addition, H2, CzH4,and C3H6are formed in lower relative yields that also depend on heating time (see Table 11). Thermolysis of 3 in silicone oil further increases the yield of CHI a t the expense of all other products. Hence, Mo-C bond homolysis is also a major initial event in this case. Solvolysis. Solvolysis of the complexes in neutral solvents is generally slow. As with 2, fusion of 3 with KOH
(8)Clark,D. N.; Schrock, R. R. J. Am. Chem. SOC. 1978, 100,6774.
M o ~ 2 *(CH&C
(3)
complexes, the solvolysis of 3 (and of 2 for comparison) was studied in glycerol solutions. After 1h at 90 "C, 13% of 2 and only 0.2% of 3 decomposed, as estimated from the yields of methane and neopentane generated. The decomposition of the complexes on heating in l-thioglycerol under otherwise identical conditions was essentially quantitative, illustrating the sensitivity of the complexes to reductive Mo-C bond cleavage. Reductive Mo-C bond cleavage with formation of methane and neopentane also occurs on reaction with alkaline NaBH4 or with ZnHC1. On reaction with concentrated H2S04,2 yields mainly ethane; a mixture of dineopentyl and neopentane is formed from 3, the reactions are complete within about 5 min. Both complexes dissolve in, and are relatively resistant to, cold glacial acetic acid; their half-life at 90 O C is about 30 min. Electronic Spectra and Photolysis. The electronic spectra of 2 and 3 are remarkably similar (see Table I). In addition to the intense absorptions due to the coordinated bpy, a previously unreported low-energy transition appearing a t 345 nm (e 2000) in 2 and at 365 nm ( 4 1900) in 3 is observed and assigned to a transition involving the 4 MO's of the C-Mo-C moiety. This assignment is supported by the observed light sensitivity of 2 and 3. Mo-C bond homolysis is apparently initiated by the transfer of an electron from the weakly bonding or nonbonding filled MO to the u* orbital. The estimated energies from the electronic spectra of 347.6 kJ.M-' for the Mo-C bonds in 2 and of 328.3 kJ.M-' of those in 3 is reasonably within the range of stability expected for Mo-C bonds. The Mo-C bonds are significantly more stable than Co-C bonds; values of 83-130 kJ-M-' were observedg for neopentylcobalamin and other organocorrins, for example. Compared to 2, the Mo-C bonds in 3 are labilized by about 20 kJ.M-', presumably due to steric effects (see below). The fact that 3 undergoes photolysis at slower rates than 2 is not in discord with this conclusion as it may be plausibly attributed to a higher efficiency of recombination. Structure. The structure of 3 (Figure 1)is of interest because it illustrates, for the first time, the effects of steric (9) Schrauzer, G . N.; Grate, J.
H.J. Am. Chem. SOC.1981,103,541.
Organomolybdenum Compounds
Organometallics, Vol. 2, No. 4, 1983 485 Table VI. Selected Bond Angles (deg)a
0(1 )-M0-0(2) N(l)-Mo-N( 2) C(ll)-Mo-C(16) O(l)-Mo-N(l) O(2)-Mo-N( 2) O(l)-Mo-N( 2) O(2 )-Mo-N( 1) O(l)-MO-C(ll) O(l)-Mo-C( 16) O(2)-Mo-C( 11) O(2)-Mo-C(16) 0-Mo-C N( l)-Mo-C( 11) N(l)-Mo-C(16) N(2)-Mo-C(11) N( 2)-Mo-C( 16) N-MO-c
110.0 (2) 68.6 (1)
145.8 (2) 87.5 (2) 92.8 (2) 156.1 (2) 161.4 (2) 102.4 (2) 101.9 (2) 96.1 (2) 97.4 (2) 99.5 (2.7) 78.5 (2) 78.8 (2) 74.2 (2) 73.8 (2) 76.3 (2.3)
Mo-N( 1)-C( 1) -N(l)-C(5) -N( 2)-C( 6 ) -N( 2 )-C( 10) Mo-C( 11)-C( 1 2 ) Mo-C(16)-C(17) C-C-C(neopenty1) C-C-C(neopenty1 C-C-C(aromatic) C-N-C(aromatic) N-C-C(aromatic) N-C-C(aromatic) C(4)-C( 5)-C( 6 ) C(5)-C(6)-C(7)
iC
122.0 (3) 119.5 (3) 121.2 (5) 120.8 (3) 118.1 (4) 119.8 (4) 109.5 (2.1) 107.1 (5)-112.2 (5) 119.1 (8) 118.2 (3) 122.2 (1.1) 115.3 (2) 124.3 (5) 122.8 (5)
For average values the average deviation from the mean is given rather than the least-squares standard deviation. Average value. Range. oms. The 0-Mo-C and N-Mo-C angles (Table IV)reveal that C(11) and C(16) bend away from N(1) and O(1) relative to N(2) and O(2). Figure 1 also shows that methyl groups (C(13), C(14), C(l8), and C(20)) are staggered around O(1) to minimize repulsive effects. Plane 2 (see Table IV), which contains the remaining six neopentyl carbons as well as O(1) and N(2), is remarkably planar (maximum deviation of O.lO(1) A for C17) and is displaced by 0.36 (1)A toward N(1) from the Mo atom. Moreover, plane 2 is essentially perpendicular to plane 1. The highly distorted octahedral coordination geometry of molybdenum in complexes 2 and 3 may be interpreted to suggest that molybdenum(V1) is in a ( 5 ~ ) ( 6 pstate ) ~ of hybridization, giving rise to a tetrahedral coordination geometry of the ( a l k ~ l ) ~ M o (moiety. O)~ Its interaction with the bpy ligand is comparatively weak and does not cause Figure 1. Perspective view of MO(O)~[CH~C(CH~)~]~(~~~) with a rehybridization to a regular octahedral geometry. the atoms numbered. Acknowledgment. This work was supported by Grant constraints imposed on dioxomolybdenum(V1) by two CHE79-50003 (G.N.S.) from the National Science FounbllUn, organic substituents in a relatively simple compound, dation. We also thank Mr. Liu Nan Hui for experimental leading to distortions which may be important factors in assistance. heterogeneously catalyzed processes. Registry No. 1, 25411-14-7; 2, 79084-25-6; 3, 83928-45-4; Whereas the (bpy)M0(0)~moieties of 2 and 3 are isoClCH&(CH,),, 753-89-9; CHI, 74-82-8; CzH4, 74-85-1; C3H6, structural and the Mo-0 and Mo-N bond distances are 115-07-1;i-C4HB,115-11-7;i-C4HI0,75-28-5;neo-C5Hlz,463-82-1; the same, the Mo-C bonds in 3 are si nificantly longer Hz, 1333-74-0. [2.236 ( 5 ) A compared with 2.191 (3) in 21, and a significant closing of the C-Mo-C angle from 149.0 ( 1 ) O in Supplementary Material Available: Tables of positional 2 to 145.8 ( 2 ) O in 3 is seen. A larger effect might have been and thermal parameters and general temperature factor exobserved had not the M0-C-C angles opened to 118.9 (9)O pressions and a listing of observed and calculated structure facton a t the methylene carbon atom to help reduce repulsion (15pages). Ordering information is given on any current masthead between the alkyl groups and the coordinated oxygen atpage.
x
