Synthesis and Reactions of an (Aryloxy) titanium (IV) Hydride

Organometallics , 1995, 14 (10), pp 4601–4610 ... The Journal of Organic Chemistry 2010 75 (15), 5083-5091 ... Synthesis and Reactivity of d Alkyl, ...
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Organometallics 1995,14, 4601-4610

4601

Synthesis and Reactions of an (Aryloxy)titanium(IV) Hydride Heinrich Noth* and Martin Schmidt Institute of Inorganic Chemistry, University of Munich, Meiserstrasse 1, 0-80333Munchen, Germany Received April 14, 1995@ Attempts to prepare (ArO)zTi(BH4)2,6 (Ar = 2,6-diisopropylphenyl), from (ArO)zTiCl2,4, and LiBH4 failed due to its decomposition by ligand exchange and reduction into (Ar0)aTi(L13-BH4), 7 , and [(ArO)Ti-(L13-(B&)2)1~,8. Reaction of 8 with trimethylphosphine gives Trimethylphosphine removes a BH3 group from 7 monomeric (ArO)Ti-(L12-(BH4)2)2PMe3,9. with formation of the hydride (ArO)3TiH*PMe3,10. This adduct releases PMe3 readily in solution, forming a n equilibrium with (ArO)aTiHwhich is attained at high rate. In spite of the weakly bonded PMe3 the unsupported hydride (hO)sTiH could not be obtained from its PMe3 adduct nor by olefin elimination from (ArO)aTiCMes,12. Hydrotitanation of alkynes to vinyltitanium compounds (Ar0)3TiCH-CHR proceeds readily and regiospecifically if polar alkynes such a s PhCsCEMes (E = Si, Sn) are used. The molecular structures of 7-10 and 12 were determined by X-ray crystallography.

Introduction Compounds of titanium(IV) play an important role in organic synthesis. They are used as reagents as well as catalysts. Outstanding examples are the McMurry reaction1 for the formation of C=C double bonds from ketones, or the epoxidation of olefinic bonds according to Sharpless,2or, as a more recent example, the Seebach r e a ~ t i o nwhich ,~ allows an enantioselective nucleophilic addition to carbonyl groups. It is the Sharpless reaction in particular which demonstrates the possibility to fix chiral alkoxides at the titanium atom in such a manner that the metal atom still remains the reactive center which influences the course of the reactions. In addition, it is well-known that hydroborations can be mediated by titanium compound^,^ and this suggests that titanium hydroborates may be the reactive species. For this reason we investigated ways to make such compounds readily available as reducing reagents with specific properties. Moreover, it is also a challenge to prepare mononuclear and polynuclear titanium hy~ possible drides unsupported by Cp or Cp* l i g a n d ~ .One way of doing so is to use amido o r RO substituents, and the present work describes some of our efforts to prepare titanium(IV)hydrides of the type (R0)3TiHwhich might be enantioselective reducing reagents if chiral substituents R are part of the RO group. To our knowledge there exist only a few representatives of titanium(IV) tetrahydroborates which are also characterized by X-ray methods. One of those is the bise- Abstract published in Aduance ACS Abstracts, July 15, 1995. (1) Mc Murry, J. E.; Fleming, M. P. J . Am. Chem. SOC.1974, 96, 4708. Betschard, C.; Seebach, D.Chimia 1989,43, 39-49. (2) Katsuki, T.; Sharpless, K. B. J. Am.Chem.Soc. 1980,102,59745976. (3) Seebach, D.; Behrend, L.; Felix, D.Angew. Chem. 1991, 103, 1383-1385. Angew. Chem., Int. Ed. Engl. 1991,30, 1008. (4)Burgess, K.; van der Donk, W. A. Organometallics 1994, 13, 3616-3620. (5) (a) Troyanov, S. I.; Antropiusova, H.; Mach, K. J . O r g a m m t . Chem. 1992,427,49-55. (b) Bercaw, J. E.; Marvich, R. H.; Bell, L. G.; Brintzinger, H. H. J . Am. Chem. SOC.1972,94, 1219-1234.

1

2

3

Figure 1. (aryloxy)titanium(IV) bis(tetrahydrob0rate) 1,6and others are the bis(amido)titanium(IV)bis(tetrahydrob0rate) 2 and the bis(amido)titanium(IV)chlorotetrahydroborate 37 (Figure 1). The common feature of these compounds is that the titanium(IV) atom is part of a ring system.

Results (Aryloxy)titanium(IV) tetrahydroborates. An obvious route to (aryloxy)titanium(IV)tetrahydroborates is the metathesis of (aryloxy)titanium(IV)chlorides with an alkali metal tetrahydroborate. The titanium chlorides are readily prepared from Tic14 and a phenol: and we synthesized (2,6-'PrzCsH30)2TiCl2, 4, by this route in boiling benzene. Reaction of 4 with LiBH4 in ether leads in the first step to the titanium(IV)chloride tetrahydroborate, 5, which can be readily recognized in an IlB NMR spectrum a t 6 -9.9. Further reaction of 5 with LiBH4 is expected to form (Ar0)zTi(BH4)2,6. As the reaction according to eq 2 proceeds a new llB NMR signal at 6 -15.6 appears, replacing the signal a t -9.9 ppm. In addition, diborane can be (6) Corazza, F.; Floriani, C.; Chiesi-Villa, A,; Guastini, C. Inorg. Chem. 1991,30, 145-148. (7) Henmann, W. A.; Denk, M.; Scherer, W.; Klingan, F. R. J. Organomt. Chem. 1993,444, C21-C24. (8) Shah, A.; Singh, A.; Mehrotra, R. C. Indian J . Chem. 1993,32A, 632. Malhotra, K. C.; Sharma, N.; Bhatt, S. S.; Chaudhry, S. C. Polyhedron 1992, 11, 2065-2068. Duff, A. W.; Kamarudin, R. A.; Lappert, M. F.; Norton, R. T. J . Chem. SOC.,Dalton. Trans. 1986,489498.

0276-733319512314-4601$09.00/00 1995 American Chemical Society

Noth and Schmidt

4602 Organometallics, Vol. 14, No. 10, 1995 detected in the solution (6(11B) +17 ppm). Two compounds crystallize from the brown solution a t -18 "C. The first and less soluble compound proved to be (2,6iPrzC&0)3TiBH4, 7; the second, more soluble compound is the turquoise-colored (2,6-'PrCsH30)Ti(BH4)2, 8. Therefore, ligand exchange and reduction set in during the course of the reaction. These processes begin after the formation of compound 5, and it is feasible that this starts with the formation of (2,6-'PrzCsH30)~Ti(BH4)2, 6, as depicted in eqs 1-3. This would comply with previous findings that reduction of Ti(IV) to Ti(111)sets in after formation of titanium(IV) bidtetrahydroborates) in reactions of titanium(IV) alkoxides with diborane in THF.g (ArO),TiCl, 4

+ LiBH, - (ArO),Ti(BH,)Cl+ 5

(ArO),Ti(BH,)Cl+ LiBH, 5

4 (ArO),Ti(BH,),

-

(1)

(ArO),Ti(BH,), 6

-

6 2(hO),Ti(BH,) 7

LiCl

+ LiCl (2)

+ [ArO-Ti(BH4),l, + BZH6 + H2 8 (3)

The fact that a llB NMR signal can be detected for compound 8 points to the conclusion that this is not a monomeric but most likely a dimeric species of type [ROTi(BH4)212with bridging RO groups. However, no BH coupling can be observed, most likely due to residual paramagnetism.1° Analysis of the IR bands in the region of the BH stretching modes reveals that the BH4 groups are ,us-bonded (via three hydrogen bridges) to the metal atom, both in compound 7 and in 8. Treatment of compound 8 with trimethylphosphine according to eq 4 yields the adduct 9 for which no llB [ArO-Ti(BH,),], 8

+ 4 PMe,

-

2ArO-Ti(BH4),*PMe3 9

(4)

NMR signal could be recorded. This is in consonance with a mononuclear Ti(II1) tetrahydroborate like Ti(BH4)3.2PMe3.11 A n X-ray structure determination of 8 confirmed the dimeric nature of this compound. Figure 2 depicts the molecular unit which has a crystallographically imposed Ci symmetry. There are two significant features of this structure. The first one is the planar four-membered T i 2 0 2 ring with a n 0-Ti-0 bond angle of 81.29". The analogous values for a dimeric Ti(IV) compound with a Ti202 core [Me2(tBu3CO)TiIVp(OMe)12amount to 70.6" with a titanium to titanium distance of 3.290(3) A.12 This is most likely a consequence of the (partial) spin pairing of the dl electrons in the dimeric Ti(II1) compound, 8 , and results in a distance between the two Ti atoms of 3.041(1)A. These data fit very well with those (9)Thomann, M. Ph.D. Thesis, University of Munich, Munich, Germany, 1992; pp 65-93. (10)Minhas, R.; Duchateau, R.; Gambarotta, S.; Bensimon, C. Inorg. Chem. 1992,31,4933-4938. (11)Jensen, J. A.;Wilson, S. R.; Girolami, G. S. J.Am. Chem. SOC. 1988,110,4977-4982. (12) Lubben, T. V.; Wolczanski, P. T. J.Am Chem. SOC.1987,109, 424-455.

Figure 2. View of the molecular structure of 8 with selected bond lengths (A) and angles (deg): Til-01, 2.005(2); Tila-01, 2.003(2); 01-C1, 1.407(3); Til-B1, 2.166(4);Til-B2, 2.162(4);Til-Tila, 3.041(1);Til-OlTila, 98.71(8);01-Til-Ola, 81.29(8);Bl-Til-B2,118.1(2k 01-Til-B1, 113.00(13);Ol-Til-B2, 113.02. Table 1. Atomic Coordinates ( x lo4) and Equivalent Isotropic Displacement Parameters (k x 10)for 8 atom

X

Y

z

U(eq)CI

TiU)

5457(5) 1278(5) 583(3) 29(2) 4421(2) 1008(2) -508(10) 28(4) B(U 4223(4) 2013(5) 1392(2) 49(9) B(2) 7358(4) 2412(5) 630(3) 48(9) C(1) 3823(3) 2139(3) -1037(15) 30(6) 2499(3) 2571(3) -1046(2) 34(6) (C(3) ')' 1962(3) 3738(4) -1555(2) 46(8) C(4) 2701(4) 4454(4) -2029(2) 50(8) C(5) 3997(4) 4000(4) -2013(2) 44(8) C(6) 4599(3) 2828(3) -1524(15) 34(6) C(7) 6012(3) 2348(4) -1561(2) 39(7) C(8) 6083(5) 1641(5) -2357(3) 65(11) C(9) 6994(4) 3689(4) -1379(3) 59(10) C(10) 1620(3) 1838(4) -533(2) 37(7) C(11) 1131(4) 3036(5) -11(2) 53(9) C(12) 446(4) 984(5) -1025(2) 5U8) a U(eq) is defined as one-third of the trace of the orthogonalized U,]tensor. O(1)

found for the T i 2 0 2 core of dimeric tris(2,6-dimethylphenoxy)titanium(III), which shows a remarkably low value for is magnetic moment.1° The second feature is the presence of pus-bonded BH4 groups, confirming the analysis of the IR data. In contrast t o the acute 0-Ti-0 bond angle we note a rather wide B-Ti-B bond angle of 118.1(2)". Thus, the Ti centers are present in a fairly distorted tetrahedral environment. Finally, one can note that the 2,6-diisopropylphenyl groups stand perpendicular to the Ti202 ring plane (see Table 1). The X-ray structure of the adduct 8.2PMe3 (9)reveals the presence of a mononuclear species in the solid state. Figure 3 depicts its molecular structure. Interestingly, the trimethylphosphine ligands occupy the apical positions of a distorted trigonal bipyramid, while the two boron atoms and the oxygen atom are part of the trigonal plane (if we neglect the bridging hydrogen atoms). The point group symmetry of 9 is C, and this symmetry is imposed by a crystallographic mirror plane

(Aryloxy)titanium(lV,, Hydride

Organometallics, Vol. 14, No. 10, 1995 4603

C13a

Table 2. Atomic Coordinates ( x lo4) and Equivalent Isotropic Displacement Parameters (A2 x 10) for 9 atom I .Y z UeaP Ti(1)

1527(4) 632(14) 1818(3) 2452(3) 1589(5) -33(2) -602(2) -1279(2) -1390(2) -824(2) -135(2) 479(3) 491(3) -499(2) -819(3) 1119(3) 1156(4) 2428(3)

O(1)

C13

c11

Figure 3. View of the molecular structure of 9 with selected bond lengths (A) and angles (deg): Til-B1, 2.457(6); Til-B2, 2.444(6);Til-P(1,2), 2.590(2);Til-01, 1.804(3);Ol-C1,1.361(5); Bl-Til-B2,121.1(2); B1-Til01,122.4(2);B2-Til-01, 116.5(2);Ol-Til-P1,93.49(3); Ol-Til-P2,93.49( 3); Til -Ol-Cl, 177.7(3);P1-Til -P2, 171.86(6). which passes through the atoms 01, Til B1, B2, the phenyl group, and the tertiary carbon atoms of the isopropyl groups. A P1-Til-Pla bond angle of 171.8(1)0 reveals a significant distortion from the ideal 180", and this is most likely due to a repulsive interaction of the PMe3 ligands with the isopropyl groups. A similar, although much less severe deviation from the ideal geometry is indicated by the B1-Til-B2 bond angle of 121.1(2)". Another interesting feature is the almost linear C1-01-Til bond angle (177.7(4)"), and this is coupled with a very short Til-01 bond length (1.804(4) A) while the C1-01 atom distance (1.368(6) A) is typical of phen01s.l~ The Ti-0bond, therefore, suggests a strong interaction between both atoms (see Table 2). This point will be discussed later. More important is the observation that the BH4 groups are bonded in a p2-fashion to the Ti center. This discerns complex 9 from complex 8. If we consider a BH4 group as a ligand similar to a halide, then we can classify compound 8 as a coordinative compound possessing a tetracoordinated Ti atom and complex 9 as being pentacoordinated. Consequently, there is more space available a t a tetracoordinated center than on a pentacoordinated atom, and this obviously determines in a first approximation whether the BH4 groups function as ,us- or ,us-ligands. This geometry is also reflected in the Ti-B bond lengths, which are 2.457(6) and 2.444(6) A in 9 and 2.162(4) and 2.166(4) A in 8, and this difference of 0.29 A fits with observations by Edelstein et al.14who first pointed out this relationship which is useful if the hydrogen positions cannot be determined unambiguosly or not at all. Moreover, these Ti-B bond lengths fit well with those found for the pzBH4 group in bis(trimethylsily1)benzamidinatotitanium(II1) tetrah~dr0borate.l~ (13)Brown, C. J. Acta Crystallogr. 1961,4 , 100-103. Powell, H. M. Acta Crystallogr. 1963,6,256-259.Skinner,J.M.;Speakmann, J. C. J. Chem. SOC.1961,185-191. (14) Edelstein, N. Inorg. Chem. 1982,20,297-299.

B(1) B(2) P(1) C(1) C(2) C(3) C(4) C(5) C(6) C(7) C(8) C(9) C(10) C(11) C(12) C(W a

2500 2500 2500 2500 675(7) 2500 2500 2500 2500 2500 2500 2500 3371(3) 2500 3376(3) 159(3) 143(4) 113(3)

1219(8) 598(3) 3694(6) -538(7) 1366(11) 76(4) 986(4) 439(5) -969(5) -1857(5) -1368(4) -2363(5) -3270(5) 2551(5) 3205(4) 2804(7) -101(7) 1451(6)

38(3) 42(7) 58(2) 63(2) 66(4) 37(10) 42(11) 51(12) 52(12) 52(12) 45(11) 64(14) 111(2) 57(13) 93(15) 134(2) 163(3) 120(2)

U(eq) is defined as one-third of the trace of the orthogonalized

U, tensor. (Arylov)titanium(IVl hydride, (Ar0)3TiH-PMe3. Treatment of (Ar0)3Ti(B&), 7, with trimethylphosphine according to eq 5 leads t o the formation of the hydride

+

(ArO),Ti(BH4) 2PMe3 6

-

(ArO),Ti-H*PMe, 10

+ H3B*PMe3( 5 )

10. Removal of the BH3 group from the tetrahydroborate without addition of PMe3 could not be achieved. The orange-colored 10 dissolves freely in hexane or toluene, but the hydride decomposes in solution at temperature above 30 "C. Moreover, the solutions turn green on prolonged exposure to sunlight with formation of Ti(II1) species. So far we have not been able to remove the coordinated phosphine in 10. For this reason an approach that would probably lead to a phosphine-free aryloxygroup-supported titanium(rV) hydride was considered, and the dehydrotitanation of a n (aryloxy)titanium(IV) alkyl seemed to be a good choice. For this reason tris(2,6-diisopropylphenoxy)titaniumchloride, 11,was reacted with tert-butyllithium according to eq 6. At 0 "C (ArO)3Ti-CI

+ tBuLi

-

(M%Ti--(

11

(6)

12

a black oil was formed, from which tris(2,6-diisopropylphenoxy)-tert-butyltitanium,12, was isolated in 30% yield as amber-colored, cube-shaped crystals. Under mass spectrometric conditions 12 looses isobutene. However, we were unable to achieve olefin elimination from 12 as shown in eq 7. A reaction sets

A (ArO),TT 12

+a

(AQ3T-H

+H2C%Me2

(7)

1On

in at about 70 "C,but the hydride obviously decomposes already at this temperature, and it could not be trapped in the presence of a scavenger like phenylacetylene.

N8th and Schmidt

4604 Organometallics, Vol. 14, No. 10, 1995

For this reason our studies exploring the chemistry of aryloxy-supported titanium(IV) hydrides had to be conducted with the PMe3 adduct 10. This compound reacts with phenylacetylene. The addition of the Ti-H bond to the CC triple bond of this alkyne does not occur stereospecifically. Two vinyltitanium complexes, 13a,b, are formed in a 1:l ratio and are characterized by the typical 13C resonance at 187.2 ppm for 13a and 207.3 ppm for 13b. Moreover, the olefinic protons are also strongly deshielded with resonances a t 7.83 and 8.92 ppm [3J(H,H)tr,, = 18.3 Hzl for 13a. Hydrolysis of 13a,b yields styrene in addition t o the phenol, and deuteriolysis produces styrene with deuterium atoms in the a-and @-positions,respectively. Much better selectivity for hydrotitanation with 10 is achieved by using silyl- or stannyl-substituted alkynes. Thus, the ratio of the Markovnikov to anti-Markovnikov addition, which leads to 14a,b, respectively, is 3:l for Me3Si-CzC-H. Stereospecificity results by using the alkynes Measi-CW-Ph or MesSn-CzC-Ph as shown in eq 8.

Table 3. Selected W P H NMR Data for the (Aryl-oxy)alkenyltitaniumCompounds (A~O)ST~[-C~R*=CSHR~I, 13a,b, 14a,b, 15, and 16, and the Alkenylzirconocene Complexesl8 Cp,ZrX[-CR1=CHR21, 17- 1 9 " 9 ~

compd 13a 13b 14a 14b 15 16

17 X=Br 18

x=c1 x = c1

19

R1 H

R2 Ph

-CaRl187.2 8.97 207.3

=C8HR2

143.81 7.87 . Ph H 122.77 6.1216.20 SiMe3 H 223.05 135.32 i155.6 Hz] 6.72lca. 7.0 H SiMeR 203.44 1127 Hzl not assigned 8.48 7.15 148.45 [143 Hzl SiMea Ph 221.38 9.09 SnMe3 Ph 223.37 152.05 [148HzJ 9.11 SiMe3 Ph 204.5 109.4 [120 Hz] 8.41 H SiMes 202.7 [128 Hzl 143.3 [136 Hzl 8.03 6.63 H Ph 177.7 [122 Hz] 140.5 [153 Hz] 7.67 6.70 ~~~

.,

a Data given in the following order: 13C chemical shift in ppm; lJ(l3C,lH)coupling constant is given in brackets followed by the 'H NMR shift. In benZened8; 17 in CD2C12.

Proof for the trans orientation of the Ti and Sn substituents comes from the l19Sn N M R spectrum. The signal a t -36.3 ppm shows the typical pattern due to l19Sn,lH coupling (3J= 177 Hz), which is incompatible with cis or geminal geometry. For these cases coupling constants of the order of 120 (cis)and 10 Hz, respectively, are to be expected.16 Additional information on the structure of the vinyltitanium compounds are obtained from a comparison with alkenylzirconium complexes CpzZr(XFCR=C(H)R', 1719.17 With certain substituents R and R , e.g., SiMe3 and Ph, an agostic interaction of the @ H atom with the Z r atom can be detected. This results in a pronounced shielding of the @ carbon atom from 150 to 110 ppm. Moreover, the coupling constant IJ(13C,lH)is reduced to about 120 Hz in the presence of an agostic interaction. The data, summarized in Table 3, clearly demonstrate that there is no agostic interaction in the (aryloxy)titanium(IV) alkenyls 13-16, which is probably due to the steric crowding a t the Ti center, and this is most likely also the reason that the vinyltitanium complexes contain no more PMe3 (Figure 4). Molecular Structures of the Trie(2,6-diisopropy1phenoxy)titanium Compounds, 7 and 12, and of Tris(2,6-diisopropylphenoxy)titaniumhydride trimethylphosphine, 10. The molecular structures of (15) Dick, D. G.; Duchateau, R. D.; Edema, J. J.H.; Gambarotta, S. Imrg. Chem. 1993,32, 1959-1963. (16) Wrackmeyer, B. Annu. Rep. NMR Spectrosc. 1986,16,73-186. (17) Hyla-Kryspin, I.; Gleiter, R.; Krtiger, C.; Zwettler, R.; Erker, G . Orgammetallics 1990,9, 517-523.

compounds 7 and 12 were determined by X-ray crystallography. They are depicted in Figures 5 and 6, their atomic coordinates and equivalent isotropic displacement parameters are shown in Tables 4 and 5, and several of their structural parameters are summarized in Table 6. The average Ti-0 and C-0 bond distances can be considered as equal in both compounds, the main difference in the T i 0 3 skeleton is found for the Ti-0-C bond angles. These are significantly larger in the tetrahydroborate than in the tert-butyl compound. This points to the conclusion that the steric influence of the tetrahydroborate group exceeds that of the tert-butyl group, and this can only be due to the bridging hydrogen atoms which are, of course, close to the titanium atom. Moreover, the Ti-B atom distance (2.204(2)A) is in accord with a pa-bonded tetrahydroborate group. Figure 7 presents the molecular structure of the hydride 10. It shows a distorted trigonal bipyramidal arrangement of the ligand atoms around the Ti center. The equatorial positions are occupied by two oxygen atoms and the hydrogen atom, while the phosphorus atom and an oxygen atom are found a t the apices of the trigonal bipyramid. (See Table 7:) The Ti-H bond length in compound 10 is 1.60(3)A. The two equatorial H-Ti-0 bond angles are significantly Werent (89.5(11) and 109.2(11)"),and this is due to the different orientation of the diisopropylphenoxy groups. More importantly, the Ti-0-C bond angle at 0 2 is 170.5(2)", approachinglinearity, while the Ti-03-C25 bond angle is only 143.4(2)" and thus significantly more bent. However, the Ti-Ol-C2 bond angle of the apical oxygen atom is 176.7(2)"and is much closer to 180"than the angle at atom 02. One may also note that the Ti-0 bond lengths become shorter as the bond angle opens. We find Ti-0 bond lengths of 1.800(3)A a t atom 0 2 and 1.848(3)A at atom 03. The longer Ti-01 atom distance of 1.811(3)A is in accord with the general and well-known fact that bond lengths to apical atoms are longer than those within the trigonal plane. This holds a t least for covalent compounds, and, therefore, com-

Organometallics, Vol. 14, No. 10,1995 4605

(Aryloxy)titanium(N) Hydride

13a

13b

1411

14b

1s

16

17

18

20

Figure 4.

C17

Fc23

C24

c4

C17 C28

Figure 5. View of the molecular structure of 7 with selected bond lengths (A) and angles (deg): Til-01, 1.774(6); Til-02, 1.781(6); Til-03, 1.781(6); Til-Bl, 2.207(13); C1-01-Til, 173.3(6); C13-02-Til, 172.2(5); C25-03-Til, 171.8(5);B1-Til-01, 110.1(4);B1-Til02, 110.2(4);B1-731-03, 111.9(4). pound 10 seems to fall into this category. If this is so, then the Ti-0 bonds should exhibit a polar covalent character involving sp-hybridized oxygen atoms 01 and 02. The more acute Ti-03-C25 bond angle has a consequence: it brings a hydrogen atom at C31 closer to the Ti atom (Ti-H distance, 2.75 A) than would be the case if the bond angle were be 180". From this point of view one may even assume that the Ti center approaches hexacoordination, and the geometrical consequence of this orientation of the H atom is reflected in the wide H-Ti-03 bond angle of 126.0(12)".

C18

Figure 6. View of the molecular structure of 12 with selected bond lengths (A) and angles (deg): Til-01, 1.786(2);Til-03, 1.799(2);Til-05, 1.803(2);C10-01Til, 167.0(2);C30-03-Til,152.7(2); C50-05-Til,154.6(2); C1-Til-01, 101.33(13); C1-Til-03, 108.81(11); C1Til-05, 102.91(12);C2-Cl-Ti1, 108.33(3). In solution, the structure of 10 is more symmetrical since there is only one set of signals in the NMR spectra for the isopropyl and phenyl groups as well as for the PMe3 ligand. At ambient temperature, the 'H NMR signal for the Ti-H proton can be detected at 6 8.5. Compared with many other metal hydrides this signal indicates a strongly deshielded proton, very similar to that of the tricyclic triamidotitaniumW) hydride 20 (6 8.29),18(Figure 8) and this is not unexpected for a metal atom with empty or fully occupied d-~rbitals.'~ A typical example is tris(2,6-diisopropylphenolato)tantalum di(18)Cummins, C. C.; Schrock, R. R.; Davies, W. M. Organometallics 1992, 11, 1452-1545. (19) Buckingham, D.; Stevens, P. J. J.Chem. Soc. 1964,2747-2759.

Noth and Schmidt

4606 Organometallics, Vol. 14, No. 10, 1995

Table 4. Atomic Coordinates ( x lo4) and Equivalent Isotropic Displacement Parameters (Az x 10) for 7 atom

X

483(7) 56(3) 1312(3) 578(3) -114(7) -344(4) -520(4) -918(6) -1158(5) -997(5) -589(4) -289(7) -56(8) -862(8) -375(5) 324(6) -911(6) 1926(4) 2154(5) 2773(6) 3163(7) 2928(6) 2298(4) 1743(6) 2041(8) 1763(9) 2059(5) 1812(8) 2613(8) 626(4) 1245(4) 1282(5) 756(7) 155(6) 7U5) 1822(5) 2283(6) 2246(6) -584(5) -1230(5) -542(5) a

Y

1472(12) 1600(5) 2161(5) -168(5) 2429(13) 1680(8) 2850(8) 289U 11) 1786(10) 624(11) 537(8) 4062(10) 5059(14) 4525(11) -726(9) -1118(10) -1748(9) 2788(7) 3108(10) 3747(13) 3964(17) 3655(14) 3029(10) 2793(12) 1595(13) 3852(15) 2695(11) 3867(13) 2061(13) - 1459(8) -2006(9) -3301(9) -4034(11) -3458(10) -2142(9) - 1200(11) -1870(14) -650(12) -1502(10) -2322(12) -953(14)

Table 6. Atomic Coordinates ( x lo4)and Equivalent Isotropic Displacement Parameters (k x 10) for 12 atom

z

1(8) 889(3) 76(4) -186(3) -896(8) 1527(5) 1817(6) 2479(6) 2811(5) 2495(5) 1853(4) 1442(8) 2019(9) 935(8) 1507(6) 1789(6) 1630(7) 142(5) 883(6) 923(6) 288(7) -432(6) -524(5) 1594(5) 1939(7) 2172(8) -1307(6) -1738(7) -1782(7) -222(4) 39(6) -9(8) -283(7) -498(6) -475(5) 331(6) 898(8) -324(6) -707(5) -619(7) -1517(6)

U(eq) is defined as one-third of the trace of the orthogonalized

U,,tensor.

hydride 21,20with d(lH) 14.86 presenting even more strongly deshielded Ta-bonded hydrogens, while the chemical shifts for zirconium-bonded hydrogen atoms are observed in the range 4-6 ppm.21 The facts that no 2J(31P,1H)coupling can be observed for the TiH protons and that only a single 31Psignal is found for the phosphine at ambient temperature points to the conclusion that the equivalence of the OR groups is not due to Berry pseudorotation but rather to an equilibrium (eq 9). (ArO),Ti-H*PMe, = (ArO),Ti- H 10 10a

+ PMe,

X

2747(5) 955(3) - 117(4) 1140(4) 622(5) 2702(2) 2379(3) 1741(4) 1401(4) 1689(5) 2324(4) 2696(4) 1427(4) 2379(6) 10(5) 3441(4) 2673(7) 4795(5) 2723(2) 3166(3) 4512(3) 4904(4) 4023(5) 2719(5) 2252(3) 5503(3) 6790(4) 5758(5) 818(4) -166(5) 621(5) 3947(2) 5017(3) 6053(3) 7132(4) 7176(4) 6142(4) 5030(3) 597x3) 7306(4) 5169(5) 3878(4) 3268(4) 4266(5) a

Y

8776(5) 7907(3) 8809(5) 6667(4) 7611(6) 9280(2) 9766(3) 11010(3) 11443(4) 10689(5) 9482(5) 8985(4) 11871(4) 12933(5) 12432(6) 7668(4) 6605(5) 7681(6) 10133(2) 11281(3) 11487(3) 12675(3) 13612(3) 13385(3) 12212(3) 10456(4) 10333(5) 10636(5) 11928(4) 13107(5) 11211(5) 7483(2) 6948(3) 6332(3) 5793(3) 5869(4) 6472(3) 7024(3) 6220(3) 6117(5) 5120(4) 7637(3) 6646(4) 8770(4)

z

UedU

7503(3) 7662(2) 7348(3) 7260(3) 8427(3) 6594(10) 5939(2) 5871(2) 5198(2) 4626(2) 4713(2) 5 363(2) 6488(2) 6491(3) 6530(3) 5433(2) 5162(3) 5075(3) 8064(10) 8254(14) 8151(2) 8330(2) 8605(2) 8713(2) 8541(2) 7866(2) 8249(3) 7084(2) 8670(2) 8622(3) 9361(3) 7745(10) 8089(2) 7688(2) 8048(2) 8770(2) 9 144(2) 8822(2) 6903(2) 6492(2) 6739(2) 9261(2) 9767(2) 9667(2)

U(eq)is defined as one-third of the trace of the orthogonalized

U, tensor.

Table 6. Comparison of Several Structural Parameters of (2,6miPrH&O)sTi(BH4/tBu), 7 and 12, in and d e e Ti-0 0-C Ti-0-C 0-Ti-0 (av) (av) Ti-C Ti-B (av) (av) 7 1.778(6) 1.372(10) 2.204(12) 173.4(5) 108.1(3) 12 1.796(2) 1.370(3) 2.095(3) 158.1(2) 114.11(9) “av” denotes the average value for chemically equivalent bonds.

(9)

Indeed, coupling can be observed at -60 “C (2J(31P,1H) = 76 Hz), and coalescence occurs at -45 “C as shown in Figure 9. Consequently, the chemical shift (6 -37) observed in the 31PNMR spectrum of 10 a t ambient temperature represents a time-averaged shielding, while (20)Visciglio, V. M.; Fanwick, P. E.; Rothwell, I. P. J. Chem SOC., Chem. Commun. 1992, 1505-1507. (21)James, B. D.; Nanda, R. K.; Wallbridge, M. G. H. Znorg. Chem. 1967,6,1979. Manriquez, J.; Mc Mister, D. R.; Sanner, R. D.; Bercaw, J. E. J.Am Chem. SOC.1978,100,2716-2725. Gozum, J. E.; Girolami, G. S. J.Am. Chem. SOC.1991,113,3829-3837. Gozum, J. E.; Wilson, S. R.; Girolami, G. S. J. Am. Chem SOC.1992, 114, 9483-9492.

the signal moves at -60 “C to -21 ppm. Addition of PMe3 to the solution of 10 shifts the resonance to higher field. No triplet for the hydride resonance due to the formation of a compound of type (Ar0)3TiH*2PMe3, which should originate by an associative exchange with an excess of PMe3, was observed. This proves not only that an equilibrium is operative but also that the equilibrium is achieved at high rate. Thus, the phosphine is not strongly bonded to the Ti atom. Consequently, this ligand can be replaced by a base exchange reaction with pyridine. However, (Ar0)3TiH~y could not be isolated due to its ready decomposition, nor was it possible t o remove PMe3 in a high vacuum. This

Organometallics, Vol. 14, No. 10, 1995 4607

(Aryloxy)titanium(IV) Hydride

@r8

Table 7. Atomic Coordinates ( x lo4) and Equivalent Isotropic Displacement Parameters (k x 10) for 10

*c39

7076(5) 5062(8) 8167(2) 7558(2) 6932(2) 8956(3) 8736(3) 9549(4) 10545(4) 10749(3) 9968(3) 10193(3) 9845(5) 11401(4) 7672(4) 6920(5) 7909(5) 7948(3) 8187(3) 8552(3) 8694(3) 8463(3) 8088(3) 7900(3) 7597(6) 8938(4) 8119(3) 9202(3) 7858(4) 6175(3) 6112(3) 5287(3) 4583(4) 4696(3) 5497(3) 5659(3) 6715(4) 4655(4) 6953(3) 7966(4) 6495(4) 3883(3) 4774(4) 4735(4)

C28

c3

5 c4

Figure 7. View of the molecular structure of 10 with selected bond lengths (A) and angles (deg): Til-H1, 1.61(3);Til-01, 1.810(3);Til-02, 1.801(2);Ti1-03,1.850(2); Til-P1, 2.613(1); C1-01-Til, 176.7(2); C13-02-Til, 170.2(2); C25-03-Til, 143.3(2); P1-Til-H1, 67.7(11); H-Til-01, 89.5(11);H-Til-02, 109.2(11). would be the best way to arrive at the unsupported hydride, (ArO)aTiH, an aim that we could not yet achieve. In contrast t o the ready detection of the Ti-bonded hydrogen atom in the molecular structure as determined by X-ray and NMR methods, it was only with difficulty that the TiH unit was detected by IR spectroscopy. A band of medium to weak intensity at 1562 cm-l was assigned to the Ti-H stretching vibration. This band is covered under bands due to CH deformation vibrations. However, if 10 was allowed to react with air, this band disappeared in difference spectra. Moreover, the assignment is further ascertained by comparing its frequency with those found for the Ti-H stretching vibrations of CpzTiH, CpzTi(H)Nz,or Cp2Ti(H)CO(14971561 cm-lLz2 Crystal data and data collection parameters for 7-10 and 12 are shown in Table 8.

a

362(3) 518(6) -52(13) 310(13) 1318(13) -349(2) -1023(2) -1275(2) -895(3) -255(3) 37(2) 739(2) 1451(3) 799(3) - 1484(3) -1437(3) -2307(3) 141(2) -621(2) -774(2) - 198(3) 544(2) 732(2) 1551(2) 2081(3) 1849(2) -1230(2) - 1248(2) -2022(2) 1821(2) 2551(2) 3041(2) 2820(2) 2113(2) 1591(2) 820(2) 825(2) 543(2) 2808(2) 3162(3) 3351(3) 496(3) -280(2) 1343(2)

7215(3) 6516(5) 7863(13) 6326(13) 7611(13) 8383(2) 8743(2) 9292(2) 9468(3) 9082(2) 8532(2) 8092(3) 8446(3) 7937(4) 8535(3) 9141(4) 8369(3) 5678(2) 5529(2) 4858(2) 4361(2) 4527(2) 5187(2) 5402(2) 4751(3) 5886(3) 6105(2) 6630(2) 5785(3) 7823(2) 7512(2) 7711(2) 8205(3) 8531(2) 8353(2) 8718(2) 9273(2) 9075(2) 7012(2) 7478(3) 6412(3) 7039(2) 5900(2) 5931(2)

U(eq) is defined as one-third of the trace of the orthogonalized

U" tensor.

Discussion The thermal stability of titanium(rV) tetrahydridoborates is rather limited and has so far only been demonstrated by the synthesis of compounds 1-3637as well as by 5 and 7 in the present study. These examples indicate that compounds of type XzTi(B&)2 are sufficiently stable against reduction to XzTi(BH4) if X2 is a chelating ligand. However, if the extra stability due to chelation is missing, compounds of type (R0)2Ti(BH4)2 either tend to be reduced readily or are stabilized as (R0)3TiBH4 by ligand exchange. This is further supported by the ease of formation of compounds of type (RZN)~T~B ~~~ or H(R0)3Ti(BH4) (R = Bu, tBug). These latter Ti(IV) tetrahydridoborates are accessible by allowing BH3THF to react with Ti(ORh9 According to the electron pair donor-acceptor concept, developed extensively by V. Gutmann, a stability order (R2N)3TiBH4 > (R0)3TiBH4 >> Hal3TiBH4 (Hal = C1, Br, I) is (22) Tacke, M.; Teuben, J. v. Private communication. (23) Mack, H. Ph.D. Thesis, University of Munich, Munich, Germany, 1995.

20

21

Figure 8. to be expected, and indeed no Hal3TiBH4 have yet been reported. The mechanism by which the Ti(IV) tetrahydridoborates decompose with concomitant reduction is still not unveiled. The most likely alternative is by loss of BH3, formation of the hydride and elimination of hydrogen as schematically depicted in eq 10.

The loss of BH3 should be favored if the Lewis acidity of the Ti(N) center increases. This would weaken the

4608 Organometallics, Vol. 14,No. 10, 1995 8.5 ppm

A

I

\

Noth and Schmidt

A)

The rather short Ti-H bond length (1.60(3) seems to be considerably shorter than for the hydrogen atoms in a Cp*Ti(H) derivative24or Ti-H-Ti bridge bonds, e.g., in @-~5:~5-fulvalene)bis@-hydrido)bis(~5-cyclopentad i e n y l t i t a n i ~ m ) In . ~ ~addition, a Ti-H bond length of 1.71 A was calculated for cp~Ti(H)SiMe3~~ in a theoretical study. The short Ti-H bond found for 10 may be a result of the electronegativity of the RO groups and the oxidation state of Ti implying a small atomic radius. A more accurate determination of the Ti-H bond lengths by neutron diffraction would be welcome, since these bond lengths cannot be determined accurately enough by X-ray methods. Nevertheless, the hydride 10,which has been fully characterized, gives evidence that even a compound &TiH unsupported by an additional ligand may be synthesized, and taking Ti-H groups on the surface of a Si02 support, an (R0)3TiH molecular hydride may finally become available.

Experimental Section [ppm]

8.60

8.41

Figure 9. Temperature dependent lH NMR spectra of the hydride resonance in 10. H-B bridging bonds and would favor the release of BH3. While this step is feasible, the mechanism of the decomposition of the postulated T i W ) hydride remains unanswered. The release of BH3 from the Ti(IV) tetrahydridoborates can be supported by a base such as pyridine or PMe3 and others. PMe3 is particularly helpful and led to the clean formation of 10. In contrast, PMe3 did not remove BH3 groups from 8 but opened Ti-0 bridging bonds of [ArOTi(BH4)212with formation of 9. One can speculate that this may be due to BH4 groups in 8 bonding to the Ti(II1)center in a more polar fashion as compared with 6. Removal of BH3 units from metal tetrahydridoborates would then be controlled by kinetics. From this point of view the fairly high thermal stability of aminotitanium(IV) tetrahydridoborates is surprising because the basic amino groups could readily attack a t the covalently bonded BH4 groups with removal of BH3. This happens indeed, but only a t temperatures exceeding 80 0C.23 Compounds of &TiBl& feature pus-bonded Bl& groups. Bond angles subtending at the Ti center, particularly the 0-Ti-0 bond angles, suggest tetracoordination with the boron atom as the fourth ligand center. This holds, in a first approximation, also for compound 8 , although the coordination numbers are, of course, 8 for 8 and 6 for 7. The titanium(II1) compound 9 is heptacoordinated by 0, P, and H atoms and features p2bonded BH4 groups. On the other hand, the B-Ti-B bond angle as well as the P-Ti-P bond angles suggests a trigonal-bipyramidal structure. Thus the results of the molecular structures as determined by X-ray methods are in accord with a static model. However, in solution, the BH4 group is fluxional as demonstrated by the quintuplet structure of its llB NMR signal. This chameleon type of behavior is typical for the BH4 group as a ligand. So far we have been unable to prepare (ArO)sTiH unsupported by additional ligands such as PMe3. Nevertheless, compound 10 is the first fully characterized titanium(IV1hydride in addition to TiT"Cp2 and TiWp* hydrides.

All reactions were performed under rigorous exclusion of moisture under dinitrogen or in vacuo. Glassware was flamedried in vacuo. LiBH4 and tBuLi were used as supplied (Chemetall GmbH),2,6-diisopropylphenol(Aldrich)was used after distillation, and Tic14 (Fluka)was used without further purification. NMR JEOL 270 (lH, llB, 31P,29Si,'19Sn),JEOL 400 ('H, 13C),and Bruker AC200 PB, 31P).ESR Bruker ESP 300. Mass spectra were recorded with a CH7-VarianMAT (70 eVJ. X-ray: Siemens P4 four-circle diffractometer with lowtemperature attachment. Samples were mounted in glass capillariesby using periluoropolyether oil (Fluka),and Mo K a radiation with a graphite monochromator was used. All calculationswere performed by using the SHELXL PLUS PC package, and in the final refinement the SHELXL 93 program was employed. Synthesis of Bis(2,6-diisopropylphenolato)titanium(IV)Dichloride, 4. To a solution O f Tic14 (10.64 g, 54 mmol) in 10 mL of cc14 was added slowly a solution of diisopropylphenol (19.24 g, 108 mmol) in 25 mL of cc14. The mixture was heated at reflux for 3.5 h until HC1 evolution ceased. After the solvent was removed under reduced pressure, 4 was left as a dark red oil (25 g, 99%),soluble in benzene, toluene, hexane, and pentane. Compound 4 was used without further purification. Anal. Found for C24H34C1202Ti (M, 473.32 g/mol): C1, 16.2. Calcd:14.98). 'H NMR (CDCldCC14):6 1.26 [d, 3J(H,H) = 6.83 Hz, 24H, (CH&CH-]; 3.50 [sept, 4H, (CH&CH-]; 7.12 (m, 6H, aromatic H). 13C NMR (CDC13): 6 23.1 [(CH&CH-I; 27.5 [(CH&CH-I; 123.3 [(CH&CH-CCH-CHI; 125.3 [(CH,)&H-C-CH]; 138.1 [(CH3)2CH-C]; 165.8 (C-0-1. Reaction of Bis(2,6-diisopropylphenolato)titanium Dichloride, 4, with LiBH4. Bis(2,6-diisopropylphenolato)titanium(IV)dichloride (8.74 g, 18.5 mmol) was dissolved in 40 mL of hexane and cooled with an ice bath, and 57 mL of a 0.64 M solution of LiBH4 in diethyl ether was added slowly with stirring. Stirring was continued for 2 h, and the precipitated LiCl was removed by centrifugation. The solvent was stripped off, and the black green solid was redissolved in 50 mL of hexane. Some insoluble material was removed by filtration,and the solution was reduced in vacuo to 30 mL and subsequently cooled to -18 T. After 18 h 10 mg of a dark red substance was isolated by filtration. We assume, that this is the etherate 6.2Et20 on the basis of the 'H NMR signal intensities. llB NMR (EtzOhexane): 6 -15.6. 'H NMR (24) You, Y.; Wilson, S. R.; Girolami, G. S. Organometallics 1994, 13,4655-4657. (25) Harrod, J. F.; Ziegler, T.;Tschinke, V. Organometallics 1990, 9, 897-902.

Organometallics, Vol. 14,No.10, 1995 4609

(Aryloxy)titanium(W) Hydride

Table 8. Crystal Data and Data Collection Parameters compd formula fw cwst dimens, mm3 cryst syst space group a, A b, A

7 C36H55B03Ti 594.52 0.41 x 0.4 x 0.4 orthorhombic Pna21 19.532(30) 10.611(16) 17.555(25) 90 90 90 3638.3(94) 1.085 4 223 6680 3161 2591 2 370 0.087113.3771 0.0724 0.1826

c, A .

a,deg

P?deg Y deg 7

v, A3

e(calcd),g cm-l

z

temp, K no. of reflns collcd no. of unique reflns no. of obsd u test no of params weighting scheme," xly final R (4u) final wR2 a

+

+

8 Cz4H~oB40zTi 510.31 0.65 x 0.45 x 0.4 monoclinic P21/n 10.196(3) 8.719(2) 17.484(4) 90 101.33(3) 90 1524.0(7) 1.093 2 213 2663 2344 1876 4 220 0.084210 0.0460 0.1162

9

C18H43B20P~Ti 406.99 0.4 x 0.4 x 0.3 orthorhombic Pnma 19.003(7) 14.153(6) 9.671(6) 90 90 90 2601.0(22) 1.039 4 213 3922 1892 1330 4 146 0.0553/1.3813 0.0437 0.1066

10 C3gH6103PTi 656.77 0.6 x 0.5 x 0.4 monoclinic P2 1/c 12.072(4) 17.588(7) 18.327(7) 90 97.38(2) 90 3859.0(25) 1.130 4 173 5762 4938 3970 2 419 0.0634l3.4425 0.0475 0.1099

12 C40Hm03Ti 636.79 0.45 x 0.33 x 0.28 t~clinic P1 10.175(2) 10.340(1) 19.024(2) 87.48(1) 86.91(1) 85.64(2) 1991.2(5) 1.062 2 293 6789 6178 4205 4 412

0.05W0.6973 0.0531 0.1228

+

w-' = a2FO2 (XP)~y P P = (Fo2 2Fc2)/3.

(CsDs): 6 1.16 [t, 12H, H~C-CHZO];1.20 [d, 3J(H,H)= 5.67 Hz, 24H, (H3C)zCH-I; 1.4 (b, BH,); 3.31 (quart, 8H, CHz-O), 3.77 [sept, 3J(H,H) = 6.75 Hz, 4H, (H3C)zCH-I; 6.9-7.2 (m, 6H,aromatic H). The brown solution was then kept for 3 days at -18 "C. After this period orange crystals of 7 had separated and were isolated by filtration. Yield: 0.9 g (16%), mp: 99-104 "C. Anal. Found for C36H55B03Ti (M, 594.52 g/mol): C, 72.22; H, 7.60. Calcd: C, 72.73; H, 9.32. llB NMR (EtzOhexane): 6 -14.6 [quint, lJ(B,H) = 88 Hz]. IH NMR (CDC13): 6 1.11[d, 3J(H,H)= 6.87 Hz, 36H, (CH3)zCH-1; 2.0 (b, BH4); 3.50 [sept, 3J(H,H) = 6.84 Hz, 6H, (CH3)zCH-1; 6.97-7.05 (m, 9H, aromatic H). 13C NMR (CDC13): 6 23.24 [(CH3)2CH-]; 26.99 [(CH~)ZCH-];123.09, 123.16, 138.1, 165.8 (aromatic C). IR (Nujol, cm-'1: Y 2528.0 (B-Ht); 2207.4, 2195.6, 2139.9 (BHb). Finally 8 precipitated after 10 days at -18 "C from the filtrate in green, well-shaped crystals. They were isolated by filtration. Yield: 0.4 g (17%). Mp: 161-165 "C (decomp). O Z510.31 T ~ g/mol): C, 55.72; Anal. Found for C Z ~ H ~ O B ~(M, H, 9.38. Calcd: C, 56.56; H, 9.98. IlB NMR (CsDs): 6 -16.9 (b, hiiz = 500 Hz). 'H NMR (C6D6): 6 1.30 [S, 12H, (CH3)zCH-1; 3.67 [s, 2H, (CH3)zCH-I; 6.64-6.94 (aromatic H). IR (Nujol, cm-'1: v 2569, 2560 (B-H*); 2214, 2139, 2097, 2068 (B-Hb).

Synthesis of 2,6-DiisopropylphenoxytitaniumBis(tetrahydridoborate)bis(trimethylphosphine), 9. Bis[(2,6diisopropylphenolato)titanium(III)bis(tetrahydridoborate)], 8 (0.1 g, 0.2 mmol), was dissolved in 2 mL of toluene, and 0.1 mL of PMe3 (1 mmol) was added slowly with stirring. During a few minutes the color of the solution changed from green t o brown. The mixture was kept at -30 "C for 4 weeks. Then the solution was reduced to 1mL. After 2 days of being cooled at -30 "C crystals had separated, and these were isolated by decantation. Yield: 0.01 g (6%) of 9 as well-crystallized blackgreen needles; mp: 135-140 "C (decomp). Anal. Found for ClsH43BzOTiP2 (M, 406.99 g/mol): C, 52.43; H, 10.18. Calcd: C, 53.12; H, 10.65. No IH, 13C, or IlB NMR signals detectible. ESR: g = 1.7 (t; hyperfine coupling constant, g = 0.0022 em-'); IR (Nujol, em-'): v 2412, 2401, 2377, 2368 (BH*); 2164, 2130 (B-Hb). Synthesis of Tris(2,6-diisopropylphenoxy)titanium Chloride, 11. To a solution of 2,6-diisopropylpheno1(7.4mL, 40 mmol) in 20 mL of benzene was added a solution of Tic14 (1.4 mL, 13.3 mmol) in 30 mL of benzene. The mixture was then heated at reflux for 8 h until the HC1 evolution had ceased. The solvent was then removed by distillation, and the

orange red solid residue was dried under reduced pressure t o yield 7.2 g of 11 (90%); mp: 115-120 "C. Anal. Found for C36H5lC103Ti (M, 615.13 @;/mol):C, 69.75; H, 7.60. Calcd: C, 70.29; H, 8.36. 'H NMR (CDCl3): 6 1.13 [d, 3J(H,H) = 6.84 Hz, 36H, (CH3)2CH-]; 3.43 [sept, 3J(H,H) = 6.84 Hz, 6H, (CH&CH-I; 6.98-7.07 (m, 9H, aromatic H). 13C NMR (CDC13): 6 23.06 [(CH3)zCH-l; 27.52 [(CH3)2CH-l; 123.01, 123.76, 137.42, 163.06 (aromatic C).

Synthesis of Tris(2,6-diisopropylphenoxy)titanium-

(IV)Hydride Trimethylphosphine,10. Tris(2,6-diisopropy1phenoxy)titaniumchloride (1.29 g, 2.1 mmol) was dissolved in 30 mL of EtzO. Then LiBH4 powder (0.5 g, 23 mmol) was added. After 2 h of stirring at ambient temperature, the solvent was removed and 60 mL of hexane were added to the residue. Insoluble material was then removed by filtration, and the filtrate was reduced to 20 mL. A 1mL aliquot of PMe3 was then added at -30 "C to the clear, orange-colored solution which changed suddenly to dark red. This solution was allowed to attain ambient temperature within 20 min. After this period the color had changed again t o brown yellow. Compound 10 precipitated after 2 days from the solution at -30 "C in well-formed orange-brown crystals. These were isolated by filtration to yield 0.3 g of 10 (25%);mp: 105-110 "C (decomp). Anal. Found for C39H6103PTi (M, 656.77 g/mol): C, 71.81; H, 9.20. Calcd C, 71.32; H, 9.36. IH NMR (ds-toluene, +20 "C): 6 0.77 [s, 9H, P(CH3)zI; 1.26 [d; 3J(H,H) = 6.9 Hz, 36H, -CH(CH&]; 3.72 [sept, 3J(H,H)= 6.8 Hz, 6H, -CH(CH&]; 6.85-7.05 (m, aromatic H); 8.5 (9, lH, Ti-H). 13C NMR (C&): 6 12.37 [d, 'J(P,C) = 38 Hz, P(CH3)zl; 23.57 [-CH(CH,)z]; 27.59 [-CH(CH&]; 121.94, 123.23, 136.75, 163.56 (aromatic C). 31P(ds-toluene, -60 "C): 6 -21. 31P(dstoluene, +20 "C): 6 -37. IR (Nujol, cm-l): v 1562 (Ti-H).

Synthesis of Tris(2,6-diisopropylphenolato)-tert-butyltitanium(n3,12. Tris(2,6-diisopropylphenolato)titanium chloride (2.19 g, 3.57 mmol) was dissolved in 30 mL of pentane. A 2.55 mL aliquot of a tBuLi solution in pentane (1.4 M, 3.6 mmol) was added slowly while stirring. During this process the reaction mixture turned black. After 1 h of stirring the insoluble material was removed by filtration. The solvent was then distilled from the filtrate under reduced pressure, and the black residue was treated with 2 mL of diethyl ether. During storage of the solution a t -18 "C, 12 separated in brown yellow crystals, which were isolated by filtration and washed with 2 mL of cold EtzO. Yield: 0.7 g of 12 (30%).Anal. Found for C4&&Ti (M, 636.79 g/mol): C, 74.45; H, 10.24. Calcd: C, 75.45; H, 9.50. Wz: 637 u. Mp: 106-110 "C. IH NMR (CDC13): 6 1.06 [d, 3J(H,H) = 6.86 Hz, 36H, (CH3)zCH-

Niith and Schmidt

4610 Organometallics, Vol. 14, No. 10,1995 1; 1.57 [s, 9H, -C(CH3)3]; 3.45 [sept, 3J(H,H) = 6.82 Hz, 6H, (CH3)sCI-I-I; 6.91-7.02 (m, aromatic H). 13C NMR (CDCld: 6 22.68 [-C(CH&I; 23.73 [(CH&CH-Arl; 26.98 [(CH3hCH1; 30.48 [-C(CH&]; 122.18, 123.20, 137.63, 160.03 (aromatic C).

NMR Spectroscopic Characterization of Tris(2,B-diisopropylphenolato)(2-phenylethenyl)titnium,13% and Tris(2,6-diisopropylphenolato)( 1-pheny1ethenyl)titanium, 13b. One drop of phenylacetylene was added to a solution of the hydride (0.1 g of 10)in 0.3 mL of c6D6. The NMR spectra showed two products in the ratio 1/1. 13a: 'H NMR (C6D6): 6 1.19 [d, 3J(H,H) = 6.84 Hz, 36H, -CH(CHd21; 3.75 [sept, WH,H) = 6.84 Hz, 6H, (CHd2-CHAr]; 6.99-7.36 (m, 14H, aromatic H); 8.97,7.87 (d, V(H,H)b, = 18.1 Hz, 2H, -C(H)-CPh(H)]. I3C NMR (C6D6): 6 23.57 [(CH&CH-]; 27.81 [(CH&CH-]; 123.34, 123.45,137.64, 161.5 (aromatic C); 187.2 [Ti-C(H)=C(Ph)Hl; 143.81 [Ti-C(H)= C(Ph)Hl. 13b: 'H NMR (CsD6): 6 1.11[d, 3J(H,H)= 6.83 Hz, 36H, -CH(CH&I; 3.61 [sept, WH,H) = 6.83 Hz, 6H, (CH3hCH-I; 6.12, 6.20 [s, 2H, =CH2, 2J(H,H) coupling constant not resolved]; 6.99-7.36 (m, 14H, aromatic H). 13C NMR (C6D6): 6 23.74 [(CH&CH-I; 27.56 [(CH&CH-Ar]; 123.34, 123.52, 137.87, 161.5 (aromatic C); 122.77 [Ti-C(Ph)=CH21; 207.3 [Ti-C(Ph)-CH21. Deuterolysis of 13a,b To the NMR sample containing 13a,bwas added two drops of D20, and the sample was shaken vigorously for 1 min. Insoluble solids were removed before the 'H NMR spectrum was measured. 'H NMR (CsD6D20) of the olefinic protons of E-2-de~teriostyrene:~~ 6 5.57 [d, 3 J ( H , H h = 17.6 Hz, lH, Ph-C(H)--(D)Hl; 6.55 [dt, 3J(H,H)tr, = 17.6 Hz, V(H,D),i. x 1.5 Hz, l H , Ph-C(H)=(D)Hl. For 1deuteriostyrene: 6 5.06 [dt, 2J(H,H)ge, zz 0.8 Hz, 3J(H,D)cis= 1.6 Hz, l H , Ph-C(D)=CH21; 5.57 [dt, 'J(H,H),, 0.8 Hz, 3J(H,D)trans= 2.7 Hz, l H , Ph-C(D)=CH21.

NMR Characterizationof Tris(2,6-diisopropylphenolato)(l-(trimethylsilyl)ethenyl)titanium, 14a, and Tris(2,6-diisopropylphenolato)(2-(trimethylsilyl)ethenyl)titanium,14b. To a solution of 0.1 g of the hydride 10 in 0.3 mL was added one drop of (trimethylsily1)acetylene. The NMR spectra showed two products, 14a and 14b,in the ratio 311. 14a: 'H NMR (CsDs): 6 0.09 [s, 9H, -Si(CH&1; 1.19 [d, 3J(H,H)= 6.83 Hz, 36H, -CH(CH&]; 3.71 [sept, V(H,H) = 6.84 Hz, 6H, (CH&CH-l; 6.88-7.18 (m, 9H, aromatic H); 6.72 (s, 2H, > C-CH2, the second signal of the CH2 proton is hidden under the aromatic protons). l3C NMR (C6D6): 6 -0.32 [-Si(CH&]; 24.02 [(CH3)2CH-]; 27.50 [(CH&CH-]; 123.20, 123.58, 137.72, 161.27 (aromatic C); 135.32 [t, 'J(C,H) = 155.6 Hz, >C=CH,]; 223.05 (>C=CH2). 14b: 'H NMR (C&): 6 0.06 [s, 9H, -Si(CH&]; 1.19 [d, d ( H , H ) = 6.83 Hz, 36H, -CH(CH&]; 3.71 [sept, 3J(H,H)= (26)Yoshino,T.; Manabe, Y.; Kikuchi, Y. J. Am Chem. SOC.1964, 86.4670-4673.

6.84 Hz, 6H, (CH3)2CH-Arl; 6.88-7.18 (m, 9H, aromatic H); 8.48 [d, %T(H,H)trans = 20.5 Hz, l H , Ti--C(H)=C(SiMes)HI; 7.14 [d, 3J(H,H)ean,= 20.5 Hz, l H , Ti--C(H)=C(SiMe3)]. 13CNMR (CeD6): 6 -1.37 [-Si(CH3)31, 24.02 [(CH~ZCH-I;27.50 [(CH3)2CH-l; 123.20, 123.58, 137.72, 161.27 (aromatic C); 203.44 [d, lJ(C,H) = 127 Hz, Ti(H)C=C(H)SiMed; the signal for the B vinyl carbon of Ti-C(H)=C(H)SiMes could not be unambiguously assigned.

NMR Characterizationof Tris(2,6-diisopropylphenolato)(cis-l-(trimethylsilyl)-2-phenylethenyl)titanium,15. To a solution of l-(trimethylsily1)-2-phenylethynein 0.3 mL of CeD6 compound 10 was added until the 29SiNMR signal of the trimethylsilyl group of l-(trimethylsilyl)-2-phenylethyne at -17.9 ppm had disappeared. 'H NMR (cdhj): 6 0.22 (s, 9H, -Si(CH&), 0.80 [d, 2J(P,H)= 2.45 Hz, 9H, P(CH3)31; 1.19 [d, 3J(H,H) = 6.84 Hz, 32H, -CH(CHM; 3.73 [sept, WH,H) = 6.84 Hz, 6H, -CH(CH3)2]; 6.8-7.4 (m, 14H, aromatic HI; 9.09 [s, l H , Ti(Me3Si)C=C(Ph)HI. 13C NMR (C6Ds): 6 1.35 [-Si(CH&]; 24.03 [-CH(CH3)2]; 27.52 [-CH(CH&]; 123.26, 123.56, 137.67, 161.80 (aromatic C/2,6-diisopropylphenolate); 148.45 [d, 'J(C,H) = 143.4 Hz, Ti(Me3Si)C=C(Ph)H];221.38 [Ti(Me3Si)C=C(Ph)H]. 29SiNMR: 6 -9.42. 2D NMR ('W 13C): crosspeaks at 6 -9.09 ('H) and 148.45 (I%).

NMR Characterizationof Tris(2,6-~€iisopropylphenolato)(cie-l-(trimethylstannyl)-!2-phenylethenyl)titanium, 16. To a solution of l-(trimethylstannyl)-2-phenylethynein C6D6 was added the hydride 10 until the 119SnNMR signal of the alkyne at -67.15 ppm had disappeared. The new signals that emerged were fully compatible with the formation of 16. 'H NMR (C6D6): 6 0.20 [s, 9H, -Sn(CH&]; 0.8 [d, 2J(P,H)= 2.44 Hz, 9H, P(CH&]; 1.19 [d, 3J(H,H) = 6.84 Hz, 36H, -CH(CH&I; 3.74 [sept, WH,H) = 6.84 Hz, 6H, -CH(CH3)21; 6.93-7.53 (m, 9H, aromatic H); 9.11 [s, 3J('19Sn,H)= 176.27 Hz, 3J(l17Sn,H)= 168.46 Hz, l H , Ti(Me3Sn)C%(Ph)K]. 13C NMR (C&): 6 -5.6 [-Sn(CH&]; 23.9 [-CH(CH&]; 27.52 [-CH(CH&]; 123.25, 123.54, 137.56, 161.52 (aromatic Cl2,6diisopropylphenoxy); 152.05 [d, lJ(C,H) = 148 Hz, Ti(Me3Sn)C=C(Ph)H]; 223.37 [Ti(MesSn)C=C(Ph)H]. lr9Sn NMR: 6 -36.30 [ddec, 2J(119Sn,H)= 53.4 Hz, 3J(11gSn,Htrans) = 177 Hzl.

Acknowledgment. We are grateful to Chemetall GmbH and BASF Aktiengesellschaft for additional support of our research efforts. We also thank Mr. S. Huber and Mr. P. Meyer for recording many NMR spectra. Supporting Information Available: Tables giving crystal data and data collection and structure refinement details, bond distances and angles, and positional and thermal parameters and figures giving additional views of the structures and packing diagrams for 7-10 and 12 (49 pages). Ordering information is given on any current masthead page. OM950271W