Organometallics 1983, 2, 162-164
162
Table 11. H-D Exchange in CH,CH,OD Catalyzed b y Transition-Metal Ethoxides' distributn of , H label,b %
% H-D
catalyst Ti( O E t ) , Zr( O E t ) , Nb,( 0Et)lO Ta,(OEt), 0 Ta,(OEt),o Ta,(OEt)1 0 T a , ( O E t ) , , + C,H,Nd Ta,(OEt),, + Et,Nd W( O E t ) ,
temp, "C
exchange
CH,D
CD,H
CD,
5 21
25 41
70 32
28
39
33
38
39
23
Oe
180 200 200 180 200 220
14 18 9 23 47 55 50
200 200 200
0e.f
All runs involved 0.5 m m o l of catalyst in 50 mmol of ethanol-d f o r 1 4 h in evacuated glass tubes. Relative areas of Percent of starting d l , d Z ,d 3 resonances ( a t 6 0.98, 0.96, and 0.94, respectively) in t h e 61.4-MHz lH-decoupled 'H NMR. R u n additionally contains OD incorporated into m e t h y l group determined by area of OH resonance in 90-MHz ' H NMR. 2 . 0 mmol of amine additive. e Catalyst decomposed t o white insolubles; n o exchange detected under conditions where 1% exchange could be observed. f Ethanol was disproportionated t o diethyl ether and H,O. a
activity of the various metal amides for the reaction shown in eq 3 (Table I) roughly parallels their efficacy for H-D exchange. The regiochemistry of l-pentene insertion varied somewhat with reaction conditions, but the product always consisted of >90% N-methyl-N-(2-methylpentyl)amine, the remainder being N-methyl-N-hexylamine. We propose that the mechanism of this reaction is that shown in the Scheme I. The proposed insertion of the olefin into the strained azametallacyclopropane intermediate has precedent in the analogous reaction of an oxametallacyclopropane recently reported by Erker.'O H-D exchange in ethanol-d was catalyzed by metal ethoxides at somewhat higher temperatures (180-220 "C). 2H NMR studies indicate that deuterium is incorporated exclusively into the methyl group of ethanol.'l Even at low conversions, much of the product consists of di- and trideuterated ethanols (Table 11). The reaction with Zr(OEt), is first-order in catalyst at 185 "C, while that with Ta,(OEt),, at 180 "C appears half-order in catalyst.I2 The rate of the H-D exchange in ethanol is enhanced by addition of triethylamine or pyridine. Incorporation of deuterium exclusively into the p-position of ethanol can be rationalized in terms of the preferential formation of an oxametallacyclobutane intermediate13(eq 4). The predominance of multiply deuterated ,3ChzCLI3 M -c M
'OCH~CH~
-1
I
+
C43CH20H
(4)
CHZ-Ct42
products, especially from the Zr catalyst, suggests that further metalation of the intermediate metallacycle is fast compared with the reverse of eq 4.14 It is noteworthy in this regard that Andersen has recently observed such an effect in the stoichiometric cyclometalation of Zr and Hf (9)Noteworthy in this regard is a claim in the patent literature that insertion of olefins into the a C-H bonds of dialkylamines is promoted by a variety of transition-metal species including NbC15. German Patent 2748 293 (to ANIC S.p.A.) (10)Erker, G.;Rosenfeldt, F. J. Organomet. Chem. 1982,224,29-42. (11)In contrast, exclusive deuteration of the methylene carbon of ethanol by low-valent group 8 catalysts has been reported: Regan, S. L. J . Org. Chem. 1974,39,26C-261. Sasson, Y.;Blum, J. J. Chem. Soc., Chem. Commun. 1974,309-310. (12)The degree of aggregation of tantalum ethoxide in refluxing ethanol has been determined as 1.78 (vs. 1.98in refluxing benzene). Bradley, D. C.; Chakravarti, B. N.; Wardlaw, W. J . Chem. SOC.1956,2381-2384. (13)Given eq 4,it is intriguing that in no case have we observed the formation of ethylene, which would be the expected product of Wittigtype cleavage of the cyclometalated intermediate. (14)An alternative explanation which we cannot exclude is that deuterium incorporation occurs in a reactive intermediate in which both cyclometalation and its reverse reaction are fast relative to alkoxide exchange with solvent. However, it is known that alkoxide exchange with free alcohol is very rapid in the homoleptic transition-metal alkoxides (see ref 6).
0276-7333/83/2302-Ol62$01.50/0
amides. Thermal elimination of alkane from the complexes R2M[N(SiMe3)J2proceeded with loss of two hydrogens from the same methyl group to afford bridging carbene , derivatives, e.g., (ZrCHSiMe2NSiMe3[N(SiMe3)2]{2.15 Elimination of two hydrogens from the same methyl group has also been observed in metal alkyl chemistry.16 We have not to date demonstrated the intermolecular insertion of olefins into the C-H bond of ethanol. We have, however, observed that isomerization of 3-butenol is catalyzed by Tap (OEt)lo a t 200 "C. At 5% conversion, the product crotyl alcohol consisted >99% of the cis isomer. This stereospecificity suggests the possibility that the isomerization involves a cyclometalation of the type shown in eq 4, followed by ring enlargement to a oxametallacyclohexene intermediate. i
Acknowledgment. The skilled technical assistance of D. h4. Lattomus and J. C. Center are gratefully acknowledged. We also thank Professor Andersen for a preprint of ref 15. Registry No. Me2ND, 917-72-6; Me2NH, 124-40-3;Zr(NMe,),, 19756-04-8; Nb(NMe,),, 19824-58-9; Ta(NMen),, 19824-59-0; W2(NMe2)6,54935-70-5; W(NMe2)6, 68941-84-4; C H ~ C H Z O D , 925-93-9; Zr(OEt),, 18267-08-8; Nb,(OEt),,, 3236-82-6;Taz(OEt)lo, 6074-84-6; l-pentene, 109-67-1. (15) Planalp, R. P.; Andersen, R. A.; Zalkin, A., submitted for publication. (16)Fellmann, J. D.; Turner, H. W.; Schrock, R. R. J. Am. Chem. SOC. 1980, 102, 6608-6609. Sharp, P. R.; Holmes, S. J.; Schrock, R. R.; Churchill, M. R.; Wasserman, H. J. Ibid. 1981,103,965-966.Wengrovis, J . H.; Sancho, J.; Schrock, R. R. Jbid. 1981,103,3932-3934. (17)Chisholm, M.H.;Cotton, F. A.; Extine, M. W.; Stults, B. R. J. Am. Chem. SOC.1976,98,4477-4485.
Synthesis of a Binuclear Hafnlum Hydride Complex Which Incorporates Hybrid Multidentate Ligands Mlchael D. Fryzuk" and Hugh Davld Williams Department of Chemistry, University of British Columbia Vancouver, British Columbia, Canada V6T 1Y6 Received August 4, 1982 Summary: Disproportionation of HfCl [Nby excess HfCI, results in the forma(SiMe,CH,PMe,),] tion of the "mono" amide complex HfCI,[N(SiMe,CH,PMe,),] HfCI, which can be converted to Hf(BH,),[N(SiMe,CH,PMe,),] and Hf(BH,), by reaction with excess LiBH,. The reaction of Lewis bases with Hf(BH4), [N(SiMe,CH,PMe,),] generates the new binuclear
,
0 1983 American Chemical Society
Communications hydride derivative { Hf [N(SiMe,CH,PMe,),]
]2(H)3(BH4)3.
Transition-metal hydrides constitute a very reactive class of organometallic complexes. This is certainly true of the group 4B metals Zr and Hf for which the unique reactivity of (q5-C6H5),Zr(H)C1and (v5-C5Me5),ZrH, with olefins, acetylenes, carbon monoxide, and isocyanides has generated new vistas in organic and organometallic To extend the potentially rich chemistry of the group 4B hydrides, we have undertaken a study aimed at the synthesis of new complexes of zirconium and hafnium which incorporate hydride ligands stabilized by ancillary “hybrid” multidentate ligands3 of the type 1. These particular ancillary ligands were specifically designed to generate new types of electronic and steric environments at the metal center by combining the hard amido donor, with soft phosphine donors into a chelating array (1). Herein we describe the synthesis of a new dimeric hafnium hydride complex which contains tetrahydroborate (-BH4)ligands.
-m,
-
2
Previously,4 we reported the synthesis of zirconium(1V) and hafnium(1V) complexes which contain two hybrid multidentate ligands and have the molecular formula MC12[N(SiMe2CH2PR2),]2 2. Although the solution and solid-state structures were of stereochemicalinterest, these complexes were surprisingly unreactive toward strong nucleophiles (RMgX, RLi, LiBH4). We attributed this lack of reactivity to overcrowding at the metal center due to the incorporation of two bulky amidophosphine chelate ligands. However, we have since discovered that these complexes undergo a facile disproportionation reaction in the presence of the starting metal tetrahalide to generate “mono” derivatives which contain only one tridentate hybrid ligand per metal; this engenders a sterically less encumbered metal center which, as a result, is very reactive to strong nucleophiles. The reaction of HfC14 (19 equiv) with the “bis” derivative HfC12[N(SiMe2CH2PMe2)2]2 (2, M = Hf, R = Me) in toluene results in the formation of a yellow, sparingly soluble complex with the analytical formula Hf2C17[N(SiMe2CH2PMe2)2]5 (3). Although the low solubility of
.,*l . f! ,
,,
+
xs HfCI,
/,_Mpe2
-
1 ,N-HfClp~HfC14 Me,Si 1
Me,S!
-
L i e ,
xs LiBH4
PMP M%Si
1 1
N--Hf(BH4),
Me,S$ L
+
Hf(BH4)4
p Me,
X
-
Hf2CI,IN(SiMe2CH,PMe,),1‘
3
(1) (a) Schwartz, J.; Labinger, J. A. Angew. Chem., Int. Ed. Engl. 1976, 15,333. (b) Carr, D. B.; Schwartz, J. J. Am. Chem. SOC. 1979,101,3521. (c) Fachinetti, G.; Floriani, C.; Roselli, A.; Pucci, S. J. Chem. SOC.,Chem. Commun. 1978, 269. (2) (a) Bercaw, J. E. Adv. Chem. Ser. 1978, No. 167, 136. (b) Wolczanski, P. T.; Bercaw, J. E. Acc. Chem. Res. 1980, 13, 121. (3) Fryzuk, M. D.; MacNeil, P. A. J. Am. Chem. SOC. 1981,103,3592. (4) Fryzuk, M. D.; Williams, H. D.; Rettig, S. J., submitted for publication in Znorg. Chem. (5) 3: mp 167.5-168.5 “C; ‘H NMR (C&G,ppm) 0.99 (t, P(CHJ2, J. = 5.0 Hz), 0.87 (t, PCHai, J = 5.6 Hz),0.22 ( 8 , Si(CH3),);31P(1HJ NM! (C&, ppm relative to P(o%e), at 141.0) -3.86 ( 8 ) . Anal. Calcd for Cl,J3zsNC17Hf2PzSi2:C, 13.56; H, 3.18; N, 1.58; C1, 28.02. Found: C, 13.88; H, 3.25; N, 1.47; C1,28.30. Preliminary solution molecular weight measurements by the Signer method (isothermal distillation) give values of 1500 which is between the monomeric (885) and dimeric (1770) formulations.
(6) Marks, T. J.; Kolb, J. R. Chem. Rev. 1977, 77, 263. (7) 4: mp 119 OC dec; molecular weight (Signer, C&, 25 “C)481, theoretical 503; ’H NMR (C6D6,ppm) 1.17 (t, P(CH3)*,Jspp= 4.0 Hz), 0.94 (t, PCH2Si,J , = 6.0 Hz),0.31 (s, Si(CH3)Z),2.9 (br q, BH,, JnB= 88 Hz); 31P(1H)Nh& (C6Ds,ppm relative to external P(OMe), at 141.0) -20.03 ( 8 ) ; ‘lB NMR (C6D6,ppm relative to external B(OMe)3at -18.1) H 88 Hz);low-temperature spectra are broad and unin-27.2 (4, ‘ J ~ = formative. And. Calcd for C10H&IB3HfP2Si2:C, 24.93; H, 8.36; N, 2.90. Found: C, 24.60; H, 8.30; N, 2.77. (8) Johnson, P. L.; Cohen, S. A.; Marks, T. J.; Williams, J. M. J . Am. Chem. SOC.1978, 100, 2709 and ref 6. (9) Shaw, B. L.; Brookes, P. R. J . Chem. SOC.A 1967, 1079. (10) James, B. D.; Nanda, R. K.; Wallbridge, M. G. H. Inorg. Chem. 1967, 6, 1979.
Organometallics 1983, 2, 164-165
164
available on both the position and the binding mode of the remaining three tetrahydroborate ligands. The high symmetry of the complex in solution, as suggested by the 'H SIC!, NMR spectrum, is perhaps a result of exchange of the three -BH4moieties between the two hafnium centers; this would require a bridgingI4 -BH4 ligand at some point in the exchange process. One possible formulation is I [ (Me2PCH2SiMe2)2NlHf(BH4))2(11-H)3(~-BH4);one bridging -BH4 and two "terminal" -BH4groups. The broad 'H NMR resonances and complex IR spectrum of 5 make such a formulation ~peculative.'~ The formation of the dimeric hydride 5 and the borane adduct proceeds via a complicated mechanism involving stepwise removal of BH, by the Lewis base and at some point, a dimerization. Although we have been unable to 9 8 7 6 5 4 3 2 1 PPm isolate or identify any intermediates as yet, some are observable by 31P(1H)and 'H NMR and are under investiFigure 1. 80-MHz 'H NMR of (Hf[N(SiMe2CH2PMeJ2112gation at present. (H)3(BH4)3(5). The -BH4 resonances appear as a broad hump The hydrides of 5 do not exchange with D2 (4atm); in at -2 ppm. The C 6 D a peak is marked by an asterisk. addition 5 is not a hydrogenation catalyst for 1-hexene even at 100 atm of H2. This lack of reactivity may be due plicated sequence ensues. The addition of excess NEt3 to to the fact that each hafnium is formally nine-coordinate a toluene solution of 4 results in the quantitative pro(assuming bidsptate -BH4 ligation) and perhaps inaccesduction (by 'H NMR) of a dimeric hafnium hydride with sible to substrates.16 Synthetic routes to tetrahydrothe molecular formula (Hf[N(SiMe2CH2PMe2)2])2(H)3borate-free hafnium hydrides are in progress. (BH4)," ( 5 ) . Separation of 5 from the borane adduct H,B+-NEt3 is difficult; however, the use of PMe, as the Acknowledgment, Financial support for this research Lewis base provides >65% recrystallized yields of 5 by was generously provided by the Department of Chemistry fractional crystallization from hexane. Less basic amines and the Natural Sciences and Engineering Research such as pyridine and ethers such as tetrahydrofuran do not Council of Canada. We also thank Dr. G. M. Williams for remove BH3 from 4 suggesting that a minimum bascity is valuable discussions. required for this transformation. Further reaction of the Registry No. 2, 83634-64-4; 3, 83634-65-5; 4, 83634-66-6; 5, remaining -BH4 ligands of 5 is not observed even with 8363467-7; HFC14, 13499-05-3;LiBH4,16949-15-8;NE5,121-44-8; tetramethylethylenediamine and longer reaction times. PMe3, 594-09-2. The dimeric nature of 5 is evident from the 'H NMR (Figure 1) wherein the hydride resonance appears as a Supplementary Material Available: Full experimental details for the synthesis of 3, 4, and 5 and the infrared spectra binomial quintet at 8.68 ppm due to coupling with f o u r of 4 and 5 (4 pages). Ordering information is given on any current equivalent phosphorus nuclei; a solution molecular weight masthead page. confirms this dimeric formulation. That there are three 4
PMe
IHf [N(SiMe,CH,PMe,),l),(H),(BH,),
+
H,B-PMe3
5
hydrides per dimer is evident from the quartet observed in the 31PNMR when the methylene and phosphorusmethyl protons are selectively decoupled. As with 4, the structure of 5 is ambiguous solely on the basis of solution spectroscopic techniques. Once again, the 'H NMR spectrum is consistent with the hybrid ligand arranged in a meridional bonding mode on each hafnium in solution; however, the relative orientation of the planar tridentate ligands on each hafnium (parallel or skew) is unknown. In addition, the quintet observed for the hydride protons suggests fluxional,12bridging hydrides as is observed for Ta2C14(PMe3)4H2.13 Unfortunately, little information is (11) 5: mp 134-136 "C; molecular weight (Signer, C&6, 25 " c ) 980, theoretical 965; 'H NMR (C7D8,ppm) 8.68 (4, H M , J p = 8.6 Hz), 1.37 J = 3.4 Hz), 0.94 (t, PCH2S1, Jlpp= 4.9 Hz), 0.37 ( 8 , (t, P(CH Si(CH&$lP{%] NMR (C&, ppm relative to external (P(OM& at 141.0) -16.16 ( 8 ) ; IlB NMR (C6D6,ppm relative to external B(OMe)3at -18.1) -49.2 (br q, JiH = 95 Hz); E t (hexane, cm-') 2520 (w), 2425 (s), 2400 (w, sh), 2144 (s), 1545 ( 8 ) (B-H and Hf-H modes). Anal. Calcd for C&I,,N2B3Hf2P4Si,: C, 24.88; H, 7.41; N, 2.90; B, 3.36; P, 12.83. Found: C, 25.00; H, 7.08; N, 3.20; B, 3.69; P, 12.96. (12) Variable-temperature'H NMR studies on 5 have been inconclusive; broadening of all resonances as the temperature is lowered is observed, but no limiting low-temperature spectrum has been as yet obtained. The singlet observed" in the slP{lHJNMR broadens as the temperature is lowered (
