Polynuclear Aluminum-Magnesium Complexes. Synthesis

Oct 1, 1995 - Chung-Cheng Chang,* Bhamidi Srinivas, Mung-Liang Wu, Wen-Ho Chiang,. Michael Y. Chiang, and Chung-Sheng Hsiung. Department of ...
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5150

Organometallics 1995, 14,5150-5159

Fixation of CO2 by a Series of Ethynyl-Bridged Polynuclear Aluminum-Magnesium Complexes. Synthesis, Characterization, and Crystal Structures of [M e d @ -i-PrzN)aMg@- C W R )12 (R = C6H5, Csb-p-CH3, t-Bu, SiMe3), [ M e a @ -Et2N)2Mg@ -CECC6H5)12, { (MeN)z[Cr-OOC(i-PrzN)la}, and { ( M e d M @-OOC(i-Pr2N))212MgI Chung-Cheng Chang,* Bhamidi Srinivas, Mung-Liang Wu, Wen-Ho Chiang, Michael Y. Chiang, and Chung-Sheng Hsiung Department of Chemistry, National Sun Yat-Sen University, Kaohsiung, Taiwan, ROC Received April 10, 1995@

A series of ethynyl-bridged polynuclear aluminum-magnesium complexes, [MeA$R'N)2Mg@-C=CR)Iz (R = C6H5 (11,CsH4-p-CH3 (2), t-Bu (31, SiMea (41,C6H5 (51,C6H4-pCH3 (6);R = i-Pr (1-41,E t for (6, 611, were prepared by reaction of the aluminummagnesium tetramer [MezAl(~-i-PrzN)zMgCu-Me)]r (A)and the dimer [Me2Al@-EtzN)zMg$Me)h (B)with various substituted acetylenes. Subsequent reaction of complexes 1 and 2 with C02 gives selective insertion products, viz. { [MezAl$-i-Pr~N)zMgljA-00C(C~CR)l}~ (R = C6H5 (71, CsH4-p-CH3 (8)), and the insertion occurs a t the Mg-C bond. Reaction of compound A with COz in diethyl ether gives two different insertion products, { ( M e a ) & OOC(i-PrzN)lz}(91, a dialuminum carbamato complex, and ((MezAl>~[$-oOC(i-Pr~N))212}Mg (lo),a mixed-metal aluminum-magnesium carbamato complex. Reaction of compound B with COZgives {(Me2Al>~[$-OOC(EtzN>)212Mg} (111,and sublimation of 11 gives compound 12,((M~ZA.~)Z~~A-OOC(E~ZN)I~}. The crystal structures of 1-5, 9,and 10 were determined by single-crystal X-ray diffraction techniques. Complexes 1-5 all consist of three fourmembered rings made of two tetrahedrally coordinated Al and Mg atoms with two bridging amido groups. The ethynyl bridging groups are almost perpendicular to the Mg-Mg vector. The pertinent bonding features (d(Ca3CB) = 1.183(6)-1.204(10)A, LMg-CaWp = 142.1(7)-165.9(6)",LMg*-CaECB = 107.6(5)-131.8(7)")indicate no substantial n-interaction between the magnesium and the ethynyl groups, yet a tendency toward such interactions is noticed. The dialuminum and aluminum-magnesium mixed-metal carbamato complexes 9 and 10 result from the insertion of COZ into the metal-N bond at the bridging amido ligands. Their syntheses and structures are discussed. Introduction Activation of the inert carbon dioxide molecule is essential for its utilization. Several reactions of transition metals with C02 have opened a new area for catalytic COZ fxati0ns.l However, only a few C02 insertion reactions on main-group elements such as aluminum2and magnesium3have been reported. Their intermediate carbamato complexes are o h n not isolated Abstract published in Advance ACS Abstracts, October 1, 1995. (1)(a) Palmer, D. A.; Eldik, R. V. Chem. Rev. 1983, 83, 651. (b) Behr, A. Angew. Chem., Int. Ed. Engl. 1988,27, 661. ( c ) Braunstein, P.; Matt, D.; Nobel, D. Chem. Reu. 1988,88, 747. (d) Kolomnikov, I.

either. We have recently reported the syntheses and crystal structures of an unusual cyclic tetrameric complex, [ M ~ ~ A ~ ( ~ L - ~ - P ~ z N ) zcontaining M ~ - M ~ )tricoorI~, dinate magnesium atoms, and a linear dimer, [ M e a @ Et~NhMgCu-Me)]z,contaming tetracoordinate magnesium atoms.4 When treated with nucleophiles, these compounds undergo metathesis and insertion reaction^.^ Their reaction with COS is facile and interesting. The COz-inserted aluminum-magnesium complexes can provide useful information in understanding the mech-

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S.; Stepovska, G.; Tyrlik, S.; Vol'pin, M. E. J . Gen. Chem. U S S R (Engl. Transl.) 1974,44, 1710. (e) Darensbourg, D. J.; Kudaroski, R. A. The Activation of Carbon Dioxide by Metal Complexes. In Aduances in Organometallic Chemistry; Stone, F. G. A., West, R., Eds.; Academic Press: New York, 1983; Vol. 22, p 129. (0 Kitajima, N.; Hikichi, S.; Tanaka, M.; Moro-oka, Y. J . Am. Chem. SOC.1993, 115, 5496. (g) Kolomnikov, I. S.; Lobeeva, T. S.; Gorbachevskaya, V. V.; Aleksandrov, G. G.; Struchkov, Yu. T.; Vol'pin, M. E. J . Chem. SOC.D 1971,972. (h) Chetcuti, M. J.;Chisholm, M. H.; Folting, K.; Haitko, D. A.; Huffman, J . C. J . A m . Chem. SOC.1982,104, 2138 and a number of references cited therein. (i) Gibson, D. H.; Ye, M.; Richardson, J. F. J . A m . Chem. SOC.1992, 114, 9716. (j) Sakamoto, M.; Shimizu, I.; Yamamoto, A. Organometallics 1994, 13, 407 and references therein.

(2)Takeda, N.; Inoue, S. Bull. Chem. SOC.Jpn. 1978, 51, 3564. Kojima, F.; Aida, T.; Inoue, S. J . Am. Chem. SOC.1986,108,391. Aida, T.; Inoue, S. J . A m . Chem. SOC.1983,105, 1304. Gilman, H.; Jones, R. G. J . Am. Chem. SOC.1940, 62, 2353. Weidlein, J. J . Organomet. Chem. 1973,49,257. (3) Weidlein, J . 2.Anorg. Allg. Chem. 1970, 378, 245. Han, R.; Parkin, G. J . A m . Chem. SOC.1992,114, 748. (4) Her, T. Y.; Chang, C. C.; Liu, L. K. Inorg. Chem. 1992,31,2291. (5) (a) Her, T. Y.; Chang, C. C.; Lee, G. H.; Peng, S. M.; Wang, Y. Inorg. Chem. 1994, 33, 99. (b) Chang, C. C.; Lee, W. H.; Her, T. Y.; Lee, G. H.; Peng, S. M.; Wang, Y. J . Chem. SOC.,Dalton Trans. 1994, 221. ( c ) Chang, C. C.; Her, T. Y.; Hsieh, F. Y.; Yang, C. Y.; Chiang, M. Y.; Lee, G. H.; Wang, Y.; Peng, S. M. J . Chin. Chem. Soc. (Taipei)1994, 41, 783. (d) Chang, C. C.; Her, T. Y.; Li, M. D.; Williamson, R.; Lee, G. H.; Peng, S. M.; Wang, Y. Inorg. Chem. 1995,34, 4296.

0276-733319512314-5150$09.00/0 0 1995 American Chemical Society

Ethynyl-BridgedAluminum-Magnesium Complexes

Organometallics, Vol. 14, No. 11, 1995 5151

anism of the Grignard-COz intermediate (eq 1). The

RMgX

+ CO, - RC0,MgX

RCOOH

(1)

X = halide complexes selected in the present study of COz insertions, the aforementioned tetrameric and dimeric complexes of aluminum-magnesium, have a strong relevance to the Grignard intermediate, and their reactions with COZmay proceed through a similar intermediate. In comparison to the well-known preparation of organic acids using Grignard reagent and COz, the magnesium atom in these aluminum-magnesium complexes is more electropositive than that in the Grignard reagent.5d Therefore, it is more suitable for activation of inert molecules such as COZ. In an attempt t o investigate further the reactivity of these complexes, we have carried out the metathesis of the magnesium-alkyl bonds using substituted acetylenes. The polynuclear ethynyl-bridged aluminummagnesium complexes obtained in the present study are valuable additions t o the collection of the previously reported ethynyl-bridged complexes of aluminum,6 ber y l l i ~ mgallium, ,~ and indium.8 These complexes provide references for the study of possible n-interactions between the magnesium centers and ethynyl groups as well as reactivity toward COZinsertion reactions. In this paper, we describe the synthesis, characterization, and structural studies of the first ethynyl-bridged aluminum-magnesium complexes and their reaction with COz. Results and Discussion Synthesis and Characterization of EthynylBridged Complexes. The precursors [Med(p-i-przN>z(B)could MgOl-Meh (A) and [Med(p-EtiN>zMgCu-Me)lz be obtained by reacting equimolar quantities of M g (NRz)z9 (R = i-Pr for compound A and R = Et for compound B) with AlMe3 as reported earlier.4 The dimeric ethynyl-bridged complexes [Med@-i-PrzN)zMg(p-CW&Jlz (11, [Me2Al@-i-PrzN)zMg@-CECCsH4p-CH3)Iz (21, [Me2Al@-i-PrzN)zM~-C=CCMe3)lz(3), and [Me2Al@-i-Pr~N)zM~-C=CSiMes)lz (4) were obtained by reacting HC=CCsH5, HCN!CsH4-p-CH3, HCWCMe3, and HC=CSiMe3, respectively, with compound A. Reaction with equimolar quantities of the acetylenes thus yielded the polynuclear dimers [ M e d @-i-PrzN)zMgOl-C=CR)Izfrom diethyl ether. Similarly, the polynuclear complexes 5 and 6 were obtained from (6) For examples of ethynyl-bridged aluminum complexes, see: (a) Stucky, G. D.; McPherson, A. M.; Rhine, W. E.; Eisch, J. J.; Considine, J. L. J.A m . Chem. SOC.1974,96,1941.(b)Albright, M. J.; Butler, W. M.; Anderson, T. J.; Glick, M. D.; Oliver, J. P. J.Am. Chem. Soc. 1976, 98,3995.(c)Almenningen, A.;Fernholt, L.; Haaland, A. J.Orgunomet. Chem. 1978,155,245.(d) Mole, T.;Surtees, J . R. Aust. J. Chem. 1964, 17,1229. (e) Jeffery, E. A.; Mole, T.; Saunders, J. K. Aust. J. Chem. 1968,21,137. (0 Eisch, J. J.; Kaska, W. C. J. Organomet. Chem. 1964, 2,184. ( 7 ) For examples of ethynyl-bridged beryllium complexes, see: (a) Morosin, B.; Howatson, J . J. Orgunomet. Chem. 1971,29,7. (b)Bell, N. A.; Nowell, I. W.; Shearer, H. M. M. J. Chem. Soc., Chem. Commun. 1982,147. (8)For examples of ethynyl-bridged aluminum, gallium, and indium complexes, see: (a)Jeffery, E. A.; Mole, T. J.Organomet. Chem. 1968, 11, 393. (b) Fries, W.; Schwartz, W.; Hausen, H.-D.; Weidlein, J . J. Organomet. Chem. 1978,159,373. (c) Tecle, B.; Ilsley, H.; Oliver, J. P.Inorg. Chem. 1981,20,2335. (9)Coates, G. E.;Ridley, D. J.Chem. Soc. A 1967,56.

the reaction of equimolar quantities of HCECC6Hb and HCWC6H4-p-CH3, respectively, with compound B (Scheme 1). All of the complexes were fully characterized by lH, 13C NMR,IR, and mass spectral studies. In the 13C NMR spectra, for complex 1, both acetylide carbon atoms show absorptions a t a much lower field (C,, 6 123.15 ppm; Cp, 6 111.37 ppm) than for the free substituted acetylenes HCaGCpCsH5 (C,, 6 86.4; Cp, 6 78.3) and HCaWpCH3 (Ca, 6 86.8; Cp, 6 74.5). Similar chemical shifts for Cp have been observed in other metal a-alkynyl complexes, while Ca shifts seem to cover a much wider range. For a comparison, refer to CpzZr@-C=CCH& (Ca, 6 131.6; Cp, 6 120.01, CpzZrkC=CC&)Z (Ca, 6 141.7; Cg, 124.8),1°Me&(C=CCH3) (C,, 6 90.3; Cg, 132.92), MezGa(CsCCH3) (Ca, 6 89.8; Cp, 6 122.4),8b MezIn(C=CCH3) (C,, 6 90.9; Cp, 6 122.4),8b(dppe)Pt(C=CR) (C,, 6 107; Cp, 6 111.8) (R = Ph) (Ca, 6 91.2; Cp, 6 105.3) (R = CH3),11and Cp(C0)z(PMe3)W(C=CPh) (Ca, 6 96.3; Cp, 6 127.4).12 For complex 2, the chemical shifts of HCWCsH4-p-CH3 were observed a t 6 123.15 (Ca) and 6 111.37 ppm (Cp), for 3,those of HCW(CH& a t 6 137.97 (Ca) and 6 97.84 (Cp), for 4,those of HC=CSi(CH3)3 at 6 140.95 (C,) and 6 136.55 (Cp) for 5,those of HCWC6H5 at (Cp),6 122.45 (Ca) and 6 105.87 (Cp), and for 6, those of HCECCsH4p-CH3 at 6 119.56 (Ca) and 6 105.22 (Cp). It has been observed that the n-complexation to the additional metal center occurring in the dimerization of monozirconium acetylide complexes results in a downfield shift of ca. 100 ppm for these alkynyl resonances in comparison to the mononuclear complexes (typical examples are [CpzZ+-CWCH3)12 and [(H3C C ~ ) Z Z + - C ~ C P ~ exhibiting ) ] Z , ~ ~ 13CNMR absorptions of the p-C=CR ligands at 6 204.2 (Ca), 147.9 (Cp) and 6 227.7 (Ca), 155.4 (Cp), respectively). Interestingly, in the case of the dimeric complex [M~~A~@-C=CCH~)IZ, such drastic deshielding signals were not observed for the acetylenic carbons, where the existence of n-complexation between aluminum and the acetylenic carbons was established.6c Similarly, in the IR spectrum, for the doubly ethynyl bridged zirconium complexes [CpzZrkCWCH3)Iz and [ ( H ~ C C ~ ) Z Z ~ ( M - C = Cthe P ~ )absorpIZ~~ tions due to vclc were observed at 1875 cm-'. In the present complexes these absorptions were observed a t much higher frequencies (2025-2065 cm-') similar to the corresponding value for the [MezAl@-C=CCH3)1 dimer. Therefore, it appears the chemical shifts of the acetylenic carbons and the IR stretching frequencies of 1-6 indicate that possible weak Mg-(n-ethynyl) interactions exist in these complexes. X-ray Crystal Structures of Ethynyl-Bridged Complexes. Although polynuclear aluminum-magnesium complexes have been studied e~tensively,'~ the (10)Erker, G.; Frtimberg, W.; Benn, R.; Mynott, R.; Angermund, K.; Kriiger, C. Organometallics 1989,8, 911. (11)Sebald, A.; Wrackmeyer, B. 2.Nuturforsch. 1983,38B, 1156. (12)Kreissl, F. R.; Eberl, K.; Uedelhoven, W. Angew. Chem. 1978, 90,908. (13)Atwood, J. L.;Stucky, G. D. J. Organomet. Chem. 1968,3,53. Atwood, J. L.;Stucky, G. D. J.A m . Chem. SOC.1969,91,2538.Ziegler, K.; Holzkamp, Z. Justus Liebigs Ann. Chem. 1957,605,93.Malpass, D. B.; Fannin, L. W. J. Orgunomet. Chem. 1975,93,1. Boncella, J. M.; Anderson, R. A. Organometallics 1986,4,205. Schaverien, C. J.; Orpen, A. G. Inorg. Chem. 1991,30,4968.McDade, C.; Gibson, V. C.; Santarsiero, B. D.; Bercaw, J. E. Organometallics 1988,7, 1. MeeseMarkscheffel, J. A,; Cramer, R. E.; Gilje, J. W. Polyhedron 1994,13, 1045.

5152 Organometallics, Vol. 14,No. 11, 1995

Chang et al.

Scheme 1. Syntheses of Compounds 1-12 [Me2AI(p-NR&Mg(~-Me)l, R= i-Pr, n=4 A R=Et, n=2 B

R I

R=i-Pr9 R=Et, 12 R

R

RZI-BU,~ R=SiMe3,4

\co2

+

R=Et R=C,jH5,5 R=C6H,-p-CH,,6

R I

R

R/N\R R=i-Pr.10 R=Et, 11

first crystal structure of an aluminum-magnesium dimer was reported only re~ent1y.l~ We have carried out X-ray structural analyses of a new group of aluminum-magnesium dimers (complexes 1-6) with bridging ethynyl groups. Complexes 1-5 possess similar structural features and mainly differ by their substituents on the bridging ethynyl groups. ORTEP views of the complexes 1-5 are shown in Figures 1-5. Selected bond distances and bond angles are listed in Table 2. The skeletons of these complexes all consist of three fused four-membered rings made up of two tetrahedrally coordinated metal atoms with two bridging ligands. The two terminal rings are formed by an Al, a Mg, and two nitrogen atoms from the bridging amido groups. The bridging groups in the terminal rings are diisopropylamido groups in complexes 1-4,while in complex 5 they are diethylamido groups. The central ring is defined by two magnesium and two a-carbon atoms of the ethynyl groups. Complexes 1, 2, 4, and 5 contain inversion centers, and therefore, the central rings are planar. Complex 3 does not contain an inverse center, though the MgzCz ring is also planar. The nonplanarity of the terminal rings may result from steric repulsion in the crystalline state. The bent-ring features of the terminal rings are very similar to those of the parent tetrameric and dimeric c~mplexes.~ The possible n-complexation of the ethynyl groups to the magnesium atom is an interesting issue. Most of the known examples of Mg-ethynyl complexes involve a monomeric Mg complex with terminal ethynyl groups (14)Veith, M.; Frand, W.;Toner, F.; Lange, H. J.Orgunomet. Chem. 1987,326, 315.

exhibiting no n-interaction.15-17 Moreover, there are only two Mg-n-ethynyl complexes known, (v5-CsMefi)zTi012-7;12-C=CSiMe3)2MgC1(THF),18 the first (n-ethynyl)magnesium complex, and [(TMED)Mg&-v2-C=CPh)2(~3-v1-C=CPh)MgEt12,l9the first multinuclear (nethyny1)magnesiumcomplex. Complexes 1-5 presented here can be viewed as the first group of examples of dimeric ethynylmagnesium complexes. Their structural features along with those of other related complexes are summarized in Table 3 and discussed in the following. The Mg-Ca(ethynyl) distances ranging from 2.170(4)to 2.273(4)A give little or no clue as to the existence of n-character in Mg-ethynyl bonds since they fall in the overlapping region between Mg-(a-C) and Mg-(nC) bond lengths. The known Mg-(n-C) bond lengths in crystalline CpzMg (2.30 A),20a CpMgBrTMEDA (2.55 (175-CsMe4H)2Ti012-r2-C~SiMe~)2MpC1(TH) (2.27 (15) Geissler, M.; Kopf, J.; Weiss, E. Chem. Ber. 1989, 122, 1395. (16) Schubert, B.; Weiss, E. Chem. Ber. 1984, 117, 366. (17) Schubert, B.; Behrens,U.;Weiss, E. Chem. Ber. 1981,114,2640. (18) Troyanov, S. I.;Varga, V.; Mach, K. Organometallics 1993,12, 2820. (19) Veibrock, H.; Abeln, D.; Weiss, E. 2.Naturforsch. 1994, B49, 89. (20) (a) Bunder, W.; Weiss, E. J. Orgunomet. Chem. 1975, 92, 1. (b) Johnson, C.; Toney, J.; Stucky, G. D. J . Organomet. Chem. 1972, 40, C11. (c) Smith, K. D.; Atwood, J. L. J . A m . Chem. SOC.1974, 96, 994. (21) Metzler, N.; Noth, H. J. Orgunomet. Chem. 1993, 454, C5. (22) Horton, A. D.; Orpen, A. G. Angew. Chem., Int. Ed. Engl. 1992, 31,876. (23)Molecular Structure and Dimensions; Kennard, O., Watson, D. G., Allen, F. H., Isaacs, N. W., Motherwell, W. D. S., Pettersen, R. C., Town, W. G., Eds.; N V A Oosthoek, Utrecht, The Netherlands, 1972; Vol. Al, p 52.

Ethynyl-BridgedAluminum-Magnesium Complexes

Organometallics, Vol. 14, No. 11, 1995 5153 c13

c10

C23

Figure 1. ORTEP view of the molecule [Me&@-i-PrzN)zMg@-CsCC&,)]z(1)using 30% probability ellipsoids. c2I

c22

C28

Figure 3. ORTEP view of the molecule [Me&&-i-PrzN)nMgOl-C~C-t-Bu)lz (3)using 30% probability ellipsoids.

Figure 2. ORTEP view of the molecule [Me&@u-i-PrzN)zMg@-CECC&-p-CH3)12 (2) using 30% probability ellipsoids. and 2.28 A),and (q5-indenyl)zMg(2.26 AFoCoverlap with the typical Mg-(a-C) length (2.175-2.246 A).15-17 One might think the CzC bond length is a better criterion for Mg-(n-C) interaction due to the bond weakening resulting from donation of n-electrons into an empty orbital on the Mg atom. As shown in Table 3, the C=C distances in these n-complexes are either slightly longer than (maximum 1.26 A) or sometimes equal t o that observed in free acetylene (1.20 A). This is in agreement with the observation of Oliver and coworkersacsuggesting that the CEC length is not necessarily a good measure of n-interaction. The C s C distances in the present set of complexes range from

1.181(6)t o 1.204(10)A. These values are very close to that for free acetylene. This seems to indicate that a n-interaction is not involved in these complexes. Examination of the complexes with well-established n-character in the Mg-ethynyl bond revealed that other structural features (see below) may serve as better criteria for the existence of n-character. In those n-ethynyl-Mg complexes a t least one of the following pronounced features exists: (1)a bent C W R group, (2) a short Mg-C,(ethynyl) distance, (3) an acute Mg-C,+p angle. The last two factors put the Mg atom close t o the middle of the CEC bond, thus constituting an orientation best suited for maximum n-interaction. In the case of Gaz(p-C=CPh)zMe4acno bending of the CIC-R moiety was observed, yet a Ga-n-ethynyl interaction was concluded due to the proper orientation of gallium with respect to the ethynyl group. The unequal Mg(l)-CpCp and Mg(l*)-C,sCp angles in complexes 1-6 led to the suspicion of a possible existence of n-interaction between magnesium and ethynyl groups. The difference of these two angles is smallest in complex 3,while it is the largest in complex 5. The orientation of the bridging ethynyl groups in complex 3 is almost perpendicular to the Mg-Mg vector, which is an orientation least suitable for any appreciable n-interaction. Complex 5, in contrast, has an orientation similar to the n-orientation in Alz(p-C4!Me)zMe4.& Complex 4 is structurally similar to complex 3. However, it has the most bent CsC-R angle (172"), suggesting n-electron donation t o Mg orbitals. One may argue that packing effects (basically steric repulsion) may also be the cause of the distorted angles

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Ethynyl-BridgedAluminum-Magnesium Complexes

Organometallics, Vol. 14, No. 11, 1995 5155

Table 2. Selected Bond Distances (A>and Angles (deg) [ M ~ ~ A ~ O ~ - ~ - P ~ ~ N ) ~ M(1) ~O~-CECC~H~)IZ AI(l)-Mg(l) Al(l)-N(2) Mg( l)-N(1) Mg(l)-C(l)-C(2) C(2)-C(l)-Mg(l*) Mg(l)-Al(l)-C(9) Mg(l)-Al(l)-N(l) N(l)-Al(l)-N(2)

Al(l)-N(2) Al(l)-Mg(l) Mg(1)-Al(l)-N(l) Mg(l)-Al(l)-C(22) Mg(l)-Al(l)-C(23) N(l)-Al(l)-N(2) Al(1)-Mg(1)-Mg(l*)

2.825(2) 1.954(5) 2.152(4) 145.7(5) 126.4(5) 105.5(2) 49.5(1) 95.1(2)

1.43(1) 1.511(7) 1.181(6)

N(2)-C(21) N(l)-C(15) C(l)-C(2) C(l2)-N(l)-C(l5) Al(l)-N(2)-C(18) Mg(l)-N(l)-C(l5) C(l)-C(2)-C(3) Mg(l)-C(l)-Mg(l*)

2.859(2) 1.971(3) 48.37(9) 138.9(2) 112.1(1) 96.0( 1) 166.73(8)

113.4(5) 114.1(4) 107.4(3) 178.4(6) 87.8(2)

N(l)-C(12) N(2)-C(18)

1.501(7) 1.581(10)

N(l)-Al(l)-C(lO) Al(l)-Mg(l)-Mg(l*) Al(l)-Mg(l)-N(2) Al(l)-Mg(l)-C(l) N(2)-Mdl)-C(l)

118.1(3) 161.61(10) 43.7(1) 115.9(1) 123.9(2)

[MezAl(lc-i-PrzN)zMg(IL-CICCsH4-p-CH3)12 (2) C(l)-C(2) 1.197(5) Mg(l)-C(l) 2.170(4) C(2)-C(3) 1.462(5) Mg(WN(2) 2.149(3) Mg(l)-Mg(l*)-C(l) N(l)-Mg(l)-N(2) N(1)-Mg(l)-C(l*) N( 1)-Mg( 1)-C( 1) Al(l)-N(l)-M&l)

46.6(1) 86.0(1) 121.8(2) 117.9(1) 88.3(1)

C(3)-C(4) Mg(l)-Mg(l*) N(l)-Mg(l)-N(2) Al(l)-N(2)-Mg(l) Mg(l*)-C(l)-C(2) C(l)-Mg(l)-C(l*) Al(l)-N(l)-C(l2) N(l)-C(ll) Mg( 1)-Mg( 1*)

Al(l)-Mg(l)-N(l) 43.38(9) Al(l)-N(2)-Mg(l) Al(l)-M&l)-C(l) 146.5(1) Mg(l)-C(l)-Mg(l*) Al(l)-Mg(l)-C(l*) 123.0(1) Mg(l)-C(l)-C(2) Mg( 1*)-Mg( 1)-N( 1) 134.9(1)

1.397(8) 3.075(3) 84.9(2) 87.6(2) 126.4(5) 92.2(2) 116.9(4) 1.497(5) 3.130(2) 87.8(1) 89.6(2) 157.9(4)

[Me2Al(IL-i-PrzN)zMg(~-C~C-t-Bu)lz (3)

Al( l)-N(1) Al(2)-N(3) Mg(2)-N(3) N(l)-C(15) N(l)-Al(l)-N(2) N(3)-Al(2)-N(4) N(l)-Mg(l)-C(7) N(3)-Mg(2)-N(4) Al(l)-N(l)-Mg(l) Si(2)-C(2) Si(2)-C(4) AlW-NU) C(2)-Si(2)-C(5) N(l)-Al(l)-N(2) N(2)-4(1)-C(19) N(l)-Mg(l)-N(2) Al(l)-Mg(l) Al( 1)-N(2) Mg( 1)-N( 1) Mg(l)-Al(l)-N(l) Mg(l)-Al(l)-C(17) N(l)-Al(l)-N(2) N(l)-Al(l)-C(l8)

1.958(7) 1.977(8) 2.129(7) 1.49(1) 96.2(3) 96.1(3) 124.8(3) 86.2(3) 88.4(3) 1.865(9) 1.81(1) 1.941(9) 109.2(5) 95.9(3) 109.8(5) 85.3(3) 2.838(3) 1.946(5) 2.097(5) 47.6(2) 131.9(2) 94.5(2) 110.1(3)

N(2)-C(21) N(3)-C(29) C(3)-C(4)

1.49(1) 1.51(2) 1.47(1)

Mg(l)-N(l) Mg( 1)-C( 1) Mg(2)-C( 1)

2.132(7) 2.225(8) 2.210(9)

C(l)-C(2) C(2)-C(3) C(18)-C(20)

Al(l)-N(l)-C(l8) Mg(l)-N(l)-C(l8) Al(l)-N(2)-Mg(l) Al(l)-N(2)-C(24) Mg(l)-N(2)-C(21)

121.8(6) 111.1(6) 87.8(3) 113.2(5) 115.3(6)

Mg(2)-C(7)-C(8) N(l)-C(l8)-C(l9) N(4)-C(38)-C(39) Mg(2)-N(3)-C(29) Al(2)-N(4)-Mg(2)

[MezA1(IL-i-Pr2N)2MgO(-C~CSiMe3)I2 (4) Mg(l*)-C(1) 2.240(9) Al(l)-N(2) N(1)-C(6) 1.57(2) Mg( 1)-N( 1) N(2)-C(12) 1.49(1) Mg(l)-C(1)

1.963(9) 2.138(8) 2.214(9)

C(l)-C(2) C(6)-C(7)

117.2(3) 116.8(3) 88.0(3) 112.4(6)

C(l)-Mg(l)-C(l*) Al(l)-N(l)-C(6) Mg(l*)-C(l)-C(2) Si(2)-C(2)-C(1)

Mg(2)-N(4)-C(38) Mg(2)-N(4)-C(35) Mg(l)-C(l)-Mg(S) Mg(2)-C(l)-C(2) C(2)-C(3)-C(4)

Mg(l)-N(l)-C(S) Mg(l)-C(l)-Mg(l*) Mg(l)-C(l)-C(2) N(2)-C(12)-C(14)

106.1(5) 114.2(6) 86.2(3) 142.1(7) 109.8(8)

108.5(6) 88.0(3) 122.3(7) 116(1)

N(l)-Mg(l)-C(l) N(B)-Mg(l)-C(l) Al(l)-N(l)-Mg(l) Al(l)-N(l)-C(9)

[MezAl(lc-Et2N)zMgOc-c~cC6H5)1~ (5) 1.490(7) Mg(l)-N(2) 2.095(5) 1.494(8) Mg(l)-C(l) 2.240(7) 1.198(8) Mg(l)-C(l*) 2.157(7) 170.5(1) 123.5(2) Al(l)-Mg(l)-Mg(l*) N(l)-Mg(l)-C(l) 43.3(1) 122.4(2) Al(l)-Mg(l)-N(2) N(2)-Mg(l)-C(l) C(l)-Mg(l)-C(l*) 93.9(2) Al(l)-Mg(l)-C(l) 122.4(1) 136.3(2) 114.8(4) Mg(l)-Mg(l*)-N(2) Al(l)-N(l)-C(9) N(1)-C(9) N(2)-C(13) C(l)-C(2)

C(2)-C(3) Mg(l)-Mg(l*) C(9)-N(l)-C(ll) Mg(l)-C(l)-C(2) C(l)-C(2)-C(3) Mg(l)-Mg(l*)-C(l)

1.204(10) 1.50(1) 1.36(3) 133.6(7) 109.0(9) 117.9(8) 108.3(7) 87.9(3) 1.20(1) 1.15(2) 92.0(3) 122.7(8) 149.6(8) 172.1(8) 1.457(8) 3.002(4) 112.4(5) 107.6(5) 176.5(7) 48.1(2)

{ ( M ~ ~ A ~ ) z ~ - O O C ( ~ (-9P) ~ ~ N ) ~ I } Al(l)-O( 1) Al(l)-0(2) Al(l)-C(8) O(l)-Al(1)-0(2*) O(l)-Al(l)-C(8) O(l)-Al(l)-C(9)

1.802(4) 1.811(4) 1.936(6) 106.2(2) 107.7(2) 105.4(2)

0(2)-C(1) N(l)-C(U N(1)-C(2)

1.287(5) 1.328(6) 1.474(6)

O(l)-C(l)-0(2) N(l)-C(2)-C(4) C(3)-C(2)-C(4)

118.5(5) 111.6(6) 112.0(6)

Al(l)-C(9) 0(1)-C(1)

1.937(5) 1.278(6)

0(2*)-Al(l)-C(8)

Al(1)-0(1)-c(1) Al(l)-0(2*)-C( 1*)

108.1(2) 135.6(4) 129.7(4)

N(l)-C(5) C(2)-C(3) N(l)-C(5)-C(6) C(l)-N(l)-C(2) C(l)-N( 1)-C(5)

1.497(8) 1.500(9) 113.3(6) 120.7(5) 120.9(5)

((Me2Al)2[(lc-OOC(i-PrzN))zlzMg) (10) Al(WO(2) Al(l)-C(ll) Al(l)-0(3) Al(2)-0(6) 0(2)-Al(l)-0(3) 0(2)-Al(l)-C(l2) 0(6)-Al(2)-0(7) 0(5)-M&1)-0(8)

1.782(5) 1.937(7) 1.779(5) 1.776(5) 105.7(2) 105.2(3) 106.9(2) 112.0(2)

O(l)-C(l) 0(2)-C(1) 0(5)-C(3) N( 1 Al(l)-0(3)-C(2) Al(2)-0(7)-C(4) C( 1)-N( 1)-C(5) C(5)-N(l)-C(8)

1.250(7) 1.298(7) 1.247(7) 1.311(8) 135.6(5) 132.6(5) 116.0(7) 124.1(7)

nesium centers. However, scattered structural features consistent with Mg-n-ethynyl interactions are at least supportive of the tendency of these Mg-ethynyl moieties to acquire some n-character in their bonding scheme. The bonding mode of the bridging ethynyl group is best described principally as a two-electronthree-center bond, similarly observed in [MgRzI, (R = Me, Et).24 However, some possible Mg-n-ethynyl interaction is supported by the low-field shift in the 13C

Al(2)-0(7) Mg( 1)-O( 1) Mg( 1) -O(5) Mg( 1)- 0 ( 8 )

1.795(5) 1.903(5) 1.913(5) 1.875(4)

0(1)-Mg(l)-0(4) 0(1)-Mg(l)-0(8) Mg( 1)-0(l)-C( 1) Mg(l)-0(4)-C(2)

110.8(2) 109.1(2) 146.7(5) 151.2(5)

N(2)-C(13) N(3)-C(3) N(3)-C(22) C(3)-N(3)-C(19) C(19)-N(3)-C(22) O(l)-C( 1)-0(2) 0(6)-C(3)-N(3)

1.494(8) 1.345(8) 1.482(8) 120.0(7) 117.4(7) 121.4(8) 117.2(7)

NMR signal as well as some scattered supporting structural features mentioned above. Formation of p-Carbamato Complexes by C02 Fixation. The complexes [MezAl@-i-PrzN)zMg@C=CR)]z (R = C6H5 (11, CsH4 p-CH3 (2)) react readily with COz in hydrocarbon solvents to give in quantitative yield the white crystalline { [Me&@-i-PrzN)zMgI$u(24) Weiss,

E.J. Orgunomet. Chem. 1965, 4 , 101

5156 Organometallics, Vol. 14, No. 11, 1995 Table 3. Selected Interatomic Distances compd [(MeCp)zZr(p-C=CPh)lzU

Chang et al.

(A)and Angles (deg) for the Ethynyl-Bridged Metal Derivatives d(C,=Cp) (bridging)

LCaECp-R

1.261(2)

172.3(1)

99

172

74

1.249(7)

141.4(3)

99.5(2)

172.7(4)

75.9(3)

2.29(1) 2.40(1)

1.22(2)

177.5(16)

96.0(6)

136.6(9)

127.4(9)

2.433 @3) 2.541 2.231

1.202

178

88

2.258 0.2) 2.252 2.252 ( ~ 4 2 ) 2.265

1.209

177

88

169

97

1.220

145

91

167

96

2.268

1.217

165

96

2.281

1.223

165

96

2.05(15) 2.004

1.229(4)

168(2)

92.0(1)

158(2)

84 llO(1)

1.183(6) 1.181(6)

180(2)

86.7(3)

178.4(6)

87.8(2)

172.8(7) 145.7(5)

93.8(5) 126.4(5)

2.170(4) 2.273(4)

1.197(5)

177.6(5)

89.6(2)

157.9(4)

112.1(3)

2.192(5) 2.218(5)

1.199(5)

176.8(5)

88.2(2)

147.8(4)

122.3(4)

2.225(8) 2.201(9) 2.214(9) 2.240(9)

1.204(10)

177.0(9)

86.2(3)

142.1(7)

131.8(7)

1.180(6)

172.1(8)

88.0(3)

149.6(8)

122.3(7)

2.240(7) 2.157(7)

1.198(8)

176.5(7)

86.1(2)

165.9(6)

107.6(5)

d(M-Ca) 2.188(2) 2.431(2) 2.191(5) 2.420(5)

2.203(5) 2.232(5)

LM-Ca-M (bridge)

LM-Ca'Cp

LM-CaWfi

87 94

84

1.204(2) a

Reference 10. Reference 21. Reference 22. Reference 19. e Reference 18. f Reference 6c. 8 Reference 8c. This work. Reference

23.

00C(C=CR)l}2 (R = C6H5 (7); C&-p-C& (811, respectively. The products are fairly soluble in toluene. In their mass spectra, the molecular ion peak could not be detected but the lH, 13C NMR, IR, and elemental analysis data lead us to believe that the insertion takes place at the magnesium-carbon bond of ethynyl bridges rather than at the aluminum-nitrogen bond (Scheme 1). In the 13C NMR spectra, the absorption at 6 159 ppm was uniquely assigned to the OCO moiety. Infrared spectra of the carbamato complexes show strong absorptions in the 650 and 1560-1680 cm-' regions, assigned to the bending frequency and stretching frequency of the OCO Attempts to obtain crystal structure information failed due to decay of the sample. Reaction of COSwith Compounds A and B. The reaction of CO2 with compound A in diethyl ether yields two kinds of insertion products; one is the dialuminum carbamato complex 9 and the other is the aluminummagnesium mixed-metal carbamato complex 10. Similarly, reaction of C 0 2 with compound B gives the dialuminum-C02 insertion product 11 and subsequent sublimation of 11 gives compound 12. In all IR spectra of the compounds 9-12, vstr(02CN) at 1558 cm-l is always observed. In order to understand the detailed structure features of these compounds, we carried out the crystal structure determination of these compounds. (25) Chisholm, M. H.; Extine, M. W. J . Am. Chem. SOC.1977,99, 782. (26) Nakamoto, K. Infrared Spectra of Inorganic and Coordination Compounds; Wiley-Interscience: New York, 1970.

The dialuminum-CO2 insertion product { (MeA)&OOC(i-PrzN)I2}(9) possesses an inversion center. An ORTEP view of the molecular structure is shown in Figure 6. Selected bond distances and angles are given in Table 2. The two Al centers are bridged by two p-OOC(i-Pr2N) groups. The bridging groups are formed during the C02 incorporation process, as mentioned before. There is a pseudo-2-fold axis perpendicular to the Al-AI vector and passing through the two bridging units. The geometry of the aluminum centers is pseudotetrahedral. The bond lengths between the aluminum atom and two methyl carbons are both 1.936(6)A, which are slightly shorter than those of the parent complex A.4 The Al-0 distances of 1.802(4) and 1.811(4)A are equal to those (1.804(5), 1.817(5), 1.820(5), and 1.809(5) A) found in [ A ~ ~ O ( C ~ O H ~ NThe O ) ~O(l)-C(l) ].~~ and 0(2)-C(1) distances of 1.278(6) and 1.287(5) A, respectively, are slightly longer than the C-0 distances in the usual aldehydes and ketones (1.23 A). The C(l)-N(l) bond distance of 1.328(6)A is considerably shorter than the N(l)-C(2) and N(l)-C(5) bond distances of 1.474(6)and 1.481(6)A, indicating that the former is a double bond. The less volatile fraction, { (MezAl)z[Cu-OOC(i-PrzN))212Mg} (10)was obtained as a second product during the sublimation process. The complex 10 possesses a linear AI-Mg-AI trinuclear unit in which the central Mg atom is surrounded by four p-OOC(i-Pr2N)units. A perspec(27)Kushi, Y.; Fernando, Q.J . Am. Chem. SOC.1970,92, 91.

Organometallics, Vol. 14, No. 11, 1995 5157

Ethynyl-Bridged Aluminum-Magnesium Complexes

metrically bridge the aluminum and magnesium atoms, while the bidentate carbamato ligands are bonded slightly asymmetrically. The two Al-0 distances (1.782(5) and 1.779(5) 8,) are similar to the corresponding values of the dialuminum carbamato complex 9. In this complex also the N(WC(1) bond distance of 1.311(8)8, is considerably shorter than t h e N(l)-C(8) distance of 1.484(9) A. Conclusions We have demonstrated that the polynuclear ethynylbridged aluminum-magnesium complexes could be synthesized in a facile manner by the metathesis reaction of the magnesium-alkyl bonds of the dimeric and tetrameric complexes with acetylenes. No substantial n-bonding interactions between the magnesium atom and the ethynyl carbons were noticed, but a close tendency toward such interactions is concluded. Reaction of compounds A and B with C02 yields carbamato complexes of dialuminum and aluminum-magnesium mixed metals. The reaction of the polynuclear ethynylbridged complexes with COZgives a single product, with insertion taking place at the Mg-C center with rupture at the magnesium-carbon bond rather than at the Al-N center. Future studies will focus on the activation of the Mg-halogen and Mg-alkoxide bonds of polynuclear aluminum-magnesium compounds.

W

Figure 6, ORTEP view of the molecule {(Me2A1)2k-O0C(i-PrzN)lz (9)using 30% probability ellipsoids. c12 c9

P I C

c3 I

W C26

Figure 7. ORTEP view of the molecule {(Me&)2[@-OOC(i-PrzN))zlzMg) (10)using 30% probability ellipsoids. tive drawing of t h e molecule along with the atomlabeling scheme is scheme in Figure 7. The selected bond lengths and angles are listed in Table 2. The geometries of the AI and Mg atoms are nearly tetrahedral. The two eight-membered chelate rings around t h e Mg atoms are approximately perpendicular to each other, as expected. The diisopropylamido groups sym-

Experimental Section All experiments were carried out in an Nz-flushed glovebag, in a drybox, or in vacuo using standard Schlenk techniques.28 All solvents were distilled and degassed prior t o use. Phenylacetylene, 4-ethynyltoluene, 3,3-dimethyl-l-butyne, and (trimethylsily1)acetylene were purchased from Aldrich and were used as received. All 'H, 13C, and 27AlNMR spectra were measured on a Varian VXR-300 spectrometer. Chemical shifts are referenced to either SiMe4 ('HI or cas ('H, 6 7.15; 13C{1H}, 6 128.001, while 27Al NMR spectra were referenced to [Al(HzO),#+. Mass spectral data were obtained on a VG-7025 GC/MS/MS spectrometer; IR spectra were obtained as Nujol mulls between KBr disks on a Bio-Rad FTS-40 FT-IR spectrometer. Elemental analyses (C, H, and N) were performed a t the Analytsche Laboratorien of H. Malissa and G. Reuter GmbH, Germany. Deviations in the results from calculated values are attributed to the extremely air-sensitive and hygroscopic nature of these compounds. The starting materials [Me2A101-i-PrzN)2MgCu-Me)14 (A) and [MezA101-EtzN)zMg01-Me)l2 (B) were prepared as described el~ewhere.~ Synthesis of [Me~(lr-i-PrzN)zMg(lr-C~CCsHb)l2 (1). A solution of 0.9 g (8.4 mmol) of phenylacetylene in diethyl ether (20 cm3)was added dropwise to a solution of compound A (2.5 g, 8.4 mmol) in diethyl ether under nitrogen. The resulting mixture was stirred for 2-3 h, and the solvent was removed partially. Recrystallizationfrom diethyl ether yielded colorless crystals of 1: mp 170-172 "C; yield 90%; 'H NMR (cas)6 -0.324 (s,6H, Al(CH&), 1.40 (d, 12H, N(CH&), 1.591 (d, 12H, NCH(CH&), 3.82 (sep, 4H, NCH(CH&), 6.99 (m, l p - H , CsHs), 7.01 (m, 2 m-H, CsHS), 7.50 (m, 2 0-H, C6H5); '3C NMR (CsDs) 6 -4.00 (broad, Al(CH3)2), 27.40 (NCH(CH&), 28.20 (NCH(CH&), 48.84 (NCH(CH&), 111.37 (MgCCCsH5), 123.153 (MgCCC,&), 128.83 ( 0 4 , CsH5), 129.86 (ipso-c, C&), 132.48 (m-C, C6H5); 27AlNMR (C&) 6 160 (broad); mass spectrum (EI, 70 eV) 10 most intense mle peaks a t 142,86,57,44,124, 281, 100, 43, 101, 209; IR 2982 m, 2926 m, 2856 s, 2064 s (28) Shriver, D. F. The Manipulation of Air-Sensitive Compounds; McGraw-Hill: New York, 1969.

5158 Organometallics, Vol.14,No.11, 1995 (C=C), 1475 s, 1388 s, 1370 s cm-l. Anal. Calcd: C, 69.11; H, 10.21; N, 7.33. Found: C, 68.44; H, 10.22; N, 7.03. Synthesis of [MeaAl(lr-i-PrzN)zMg(lr.C~CC~q.CHs)lz (2). A similar procedure was adopted, except for using 4-ethynyltoluene in place of phenylacetylene. Complex 2: mp 159-161 "C; yield 90%; 'H NMR (C&) 6 -0.30 (8,6H, Al(CH&), 1.45 (d, 12H, NCH(CH&), 1.61 (d, 12H, NCH(CHdz), 1.93 (s, 3H, p-C&C&), 3.82 (sep, 4H, NCH(CHdd, 6.89 (d, 2 m-H, C6H4), 7.43 (m, 2 0-H, C6H4); I3CNMR (CeD6)6 -3.70 (broad, d(CH3)2),21.35 @-C&4CH3), 27.45 (NCH(CH&), 28.32 (NCH(CH&), 48.86 (NCH(CH&), 110.64 (MgCCCsH4CHd, 120.31 (M~CCCEH~CH~), 129.64 (m-C, C6H4), 132.54 (0-c, CsH4), 140.24 @-C,C&); 27AlNMR (C&) 6 160 (broad);mass spectrum (EI, 70 eV) 10 most intense mle peaks 44, 86, 142, 57, 124,299, 281, 194,214, 98; IR 2960 m, 2925 m, 2869 m, 2060 s (CsC), 1604 s, 1502 s, 1452 s, 1386 6, 1366 s cm-'. Anal. Calcd: C, 69.61; H, 10.40; N, 7.06. Found: C, 69.44; H, 10.34; N, 7.01. Synthesis of [MeaAl(lr-i-PrzN)zMg(Ir-CrCCMes)l2 (3) and [MeaAl(lr-i-PrzN)zMg(Ir-C~CSiMes)l2 (4). A procedure similar to that used for the complexes 1 and 2 was adopted, except for using 3,3-dimethyl-l-butyne or (trimethylsily1)acetylene. Colorless crystals were obtained upon recrystallization from diethyl ether. Complex 3: mp 169-171 "C; yield 90%; 'H NMR (C6D6) 6 -0.14 (s, 6H, Al(CH&), 1.12 (s, 9H, C(CH3)3), 1.41 (d, 12H, NCH(CH&), 1.49 (d, 12H, NCH(CH3)2), 3.78 (sep, 4H, NCH(CH&); I3C NMR (C6D6)6 -3.20 (broad, Al(CH3)2),27.70 (NCH(CH&), 29.01 (NCH(CH&), 29.17 (C(CH3)3), 30.23 (C(CH&), 48.86 (NCH(CH&), 97.85 (MgCC(CH&), 137.98 (MgCC(CH&); 27AlNMR ( c a s ) 6 155 (broad); mass spectrum (EI, 70 eV) 10 most intense mle peaks a t 44,142,86, 124,67, 57, 262, 347, 281, 292; IR 2958 m, 2926 m, 2869 m, 2053 s (C=C), 1550 s, 1462 s, 1392 s, 1367 s cm-'. Anal. Calcd: C, 66.21; H, 11.93; N, 7.72. Found: C, 65.93; H, 11.18; N, 6.87. Complex 4: mp 125 "C; yield 90%; IH NMR (C6D6) 6 -0.17 (s, 6H, Al(CH3)2),0.14 (s, 9H, Si(CH&), 1.412 (d, 12H, NCH(cH3)2),1.47 (d, 12H, NCH(CHdd, 3.78 (sep, 4H, NCH(CHd2); NMR (CsDs) 6 -3.20 (broad, &C&)Z, -0.51 (si(m3)3), 27.56 (NCH(CH&), 28.68 (NCH(CH3)z),48.77 (NCH(CHdz), 136.55 (MgCCSi(CH&), 140.95 (MgCCSi(CH3)3); 27Al NMR (C&) d 155 (broad); mass spectrum (EI, 70 ev) 10 most intense mle peaks 124,363,298, 142,43, 57,83,98,264,278; IR 2961 m, 2871 m, 2038 s (CEC), 1664 s, 1466 s, 1389 s cm-'. Synthesis of [MeaAl(lr-EtnN)zMg(lr-C~CC9I~)]z (5) and [MezAl(lr-Et~N)zMg(lr-C1Cc6H4-~-CHs)]2 (6). A solution of 0.9 g (8.4 mmol) of phenylacetylene or 0.9 g 4-ethynyltoluene in diethyl ether was added dropwise to a solution of compound B (2.0 g, 8 mmol) in ether under nitrogen. The mixture was stirred a t room temperature for 1 h, and the crude product was recrystallized from diethyl ether. Complex 5: mp 120-122 "C; yield 75%; 'H NMR (C6D6) 6 -0.42 (s, 6H, M(CH3)2),1.15 (m, 12H, N(CHzCH&), 3.11 (m, 8H, N(CH2CH3)2),6.96 (m, lp-H, C6H5), 6.97 (m, 2 m-H, C6H5), 7.53 (m, 2 o-H, C&); NMR (CsDd 6 -9.87 (broad, Al(CH3)2), 13.69 (N(CH2CH&), 40.29 ( ( N C H Z C H ~ )105.87 ~, (MgCCC&,),122.45 (M&CC&J, 125.80 (2 0-c,c a s ) , 129.77 (ipso-C, C&), 132.48 (m-C, C6H5); 27Al NMR (C6D6) 6 160 (broad): mass spectrum (EI, 70 eV) 10 most intense mle peaks 44, 58, 73, 96, 102,114, 196, 311,451, 638; IR 2980 m, 2920 m, 2856 m, 2060 s (CzC), 1600 s, 1500 s, 1450 s, 1380 8,1375 s cm-'. Anal. Calcd: C, 66.15; H, 9.49; N, 8.57. Found: C, 66.04; H, 9.32; N, 8.45. Complex 6: mp 132-134 "C; yield 75%; 'H NMR (C&) 6 -0.41 (s, 6H, Al(CH3)2), 1.18 (m, 12H, N(CHzCH&), 1.93 (8, 3H, p-C6H4CH3),3.140 (m, 8H, N(CH&H&), 6.82 (d, 2 m-H, CsH4), 7.47 (d, 2 0-H, C6H4); I3C NMR (CsD6) 6 -9.93 (Al(CH3)z),k 21.31 (CsH4-p-CH3), 40.32 (NCHzCHa), 13.72 (NCHZCH~), 105.22 (MgCCCsHdCH3),119.56 (MgCCC&4CH3), 129.63 (2 m-C, C6H4), 132.56 (2 0-c, C&), 140.13 (2 p-c, C6H4); 27AlNMR (CsD6) 6 155 (broad); mass spectrum (EI, 70 eV) 10 most intense mle peaks at 58, 73, 96, 115, 128, 210,

Chang et al. 325,479,608,666; IR 2970 m, 2920 m, 2850 m, 2025 s (CIC), 1470 s, 1390 s cm-1. Anal. Calcd: C, 66.96; H, 9.69; N, 8.22. Found: C, 66.78; H, 9.52; N, 7.98. {MeaAl(Ir~i-PraN)eMg[-OOC(CrCR)l}~(R = C6Ha (7), Csft-p-C& (8)). A solution of complex 1 or 2 in benzene was transferred to a three-necked Pyrex flask (100 cm3)equipped with one inlet for N2 and another for bubbling dry COZgas. Dry COz is bubbled through the stirred solution for 20 min, and the resulting crude product upon removal of solvent was recrystallized from toluene to obtain transparent crystals. Compound 7: mp 160 "C dec; yield 70%; '€3 NMR (CsDs) 6 -0.037 (9, 6H, Al(CH&), 1.36 (d, 12H, NCH(CH&), 1.40 (d, 12H, NCH(CH&), 3.77 (sep, 4H, NCH(CH&), 6.843 (m, 1p-H, C6H5), 6.88 (m, 2 m-H, C&), 7.84 (m, 2 o-H, C6H5); NMR (C6D6) 6 -4.15 (broad, Al(CH3)2), 26.43 (NCH(CH&), 26.72 (NCH(CH&), 47.84 (NCH(CH&), 84.23 (MgCCC&), 85.38 (M&CC&), 119.92 (2 0-c, C6H5), 130.29 (ipso-c, C&), 133.04 (2 m-C, C6H5), 159.36 (OCO);27AlNMR (C6D6) 6 160 (broad); mass spectrum (EI, 70 eV) 10 most intense mle peaks 44,57,71,86,91,101,129,142,214,299; IR 2960 m, 2920 m, 2876 m, 2210 s (CEC), 1590 s, 1500 s, 1465 s, 1381 s cm-'. Anal. Calcd: C, 64.75; H, 9.10; N, 6.56. Found: C, 64.47; H, 8.90; N, 6.31. Complex 8: mp 125 "C dec; yield 75%; 'H NMR (CsDs) 6 -0.028 (s, 6H, Al(CH3)2), 1.37 (d, 12H, NCH(CH3)z),1.42 (d, 12H, NCH(CH&), 1.85 (s, 3H, CsH4-p-CH3), 3.79 (sep, 4H, NCH(CH&), 6.70 (d, 2 m-H, C6H4), 7.43 (m, 2 o-H, C6H4); NMR (C6Ds) 6 -3.79 (broad, Al(CH3)2), 21.32 (Cs&-p-CH3), 26.80 (NCH(CH&), 27.08 (NCH(CH3)z),48.18 (NCH(CH3)z), 84.352 (MgCCCa&H3), 86.25 (MgCCC&CH3), 117.23 (ipsoC, C&), 129.58 (2 m-C, C&), 159.89 (oca); z7AlNMR (CsDs) 6 160 (broad), mass spectrum (EI, 70 eV) 10 most intense mle peaks 86, 44, 91, 101, 142, 115, 186, 228, 241, 298; IR 2967 m, 2925 m, 2874 m, 2210 s (CsC), 1590 s, 1508 s, 1463 s, 1381 s cm-1. Anal. Calcd: C, 65.40; H, 9.30; N, 6.35. Found: C, 65.21; H, 9.39; N, 6.56. ((MeaAl)z[lr-OOC(i-PrzN)lz} (9) and {(MeaAl)z[(lr-OOC(i-Prfl))&Mg} (10). Compound A (2.5 g, 13 mmol) was dissolved in 75 cm3of diethyl ether. C02 was bubbled through the solution for 40 min, and the solvent was removed under vacuum. Sublimation of the crude product gave two colorless crystals, complex 9 at 120 "C and another crystal at 135 "C (complex 10). Complex 9: 'H NMR (CsD6) 6 -0.22 (s, 12H, &(CH3)3), 0.92 (d, 24H, NCH(CH&), 3.61 (sep, 4H, NCH(CH&); NMR (CsD6) 6 -10.73 (broad, A(CH3)2), 20.21 (NCH(CH~)Z), 47.19 z7Al NMR (CsDd 6 140 (broad), (NCH(CH&), 157.97 (OCO); mass spectrum (EI, 70 eV) 10 most intense mle peaks 387,371, 315, 244, 186, 144, 128, 102, 86, 43; IR 2921 (m), 1558 (s, br), 1496 (m), 1362 (s), 1214 (s), 1180 (s), 1157 (SI, 1086 (s) cm-l. Anal. Calcd: C, 53.72; H, 10.08; N, 6.96. Found: C, 53.12; H, 9.92; N, 7.47. Complex 10: mp 133-135 "C; 'H NMR (C&) 6 -0.241 (s, 12H, Al(CH3)), 1.07 (d, 48H, NCH(CH&), 2.80 (m, br, 8H, , NCH(CH&; 13CNMR (c&3)6 -10.42 (broad, M ( a 3 ) 2 ) 20.65 (NCH(CH&), 46.48 (NCH(CH&), 159.41 (OCO); 27AlNMR 6 140 (broad); mass spectrum (EI, 70 eV), 10 most intense mle IR 2910 peaks 685,556,498,387,315,244,186,144,102,86; (m), 1550 (s, br), 1561 (s, br), 1480 (m), 1356 (s), 1217 (91, 1176 (s), 1070 (8) cm-l. Anal. Calcd: C, 53.57; H, 9.58; N, 7.83. Found: C, 52.70; H, 9.25; N, 7.71. {(MeaAl)z[((r-OOC(EtzN))~lzMg} (11) and {(MeaAl)z[lr00C(Et&)12} (12). C02 was bubbled through a solution of compound B dissolved in diethyl ether for 45 min. The precipitated magnesium salt was removed by filtration, and the filtrate was reduced under vacuum. The crude product was recrystallized from diethyl ether to give colorless needles of 11: mp 100-101 "C; yield 40%; 'H NMR (C6D6) 6 -0.24 (s, 12H, A(CH3)2),0.88 (t,24H, NCHZCH~), 3.01 (m, 16H, NCHZCH3); I3C NMR (C&3)6 -10.58 (AlCH&), 13.47 (NCHZCH~), 42.01 (NCH2CH3), 159.83 (OCO); 27Al NMR (C6D6) 6 140 (broad); IR 2923 (m), 1572 (s, br), 1485 (m), 1358 (s), 1213 (s),

Organometallics, Vol. 14,No. 11, 1995 5159

Ethynyl-Bridged Aluminum-Magnesium Complexes 1182 (s), 1162 (SI, 1075 (5). Anal. Calcd: C, 48.55; H, 9.25; N, 8.10. Found: C, 48.10; H, 9.12; N, 7.95. The crude product 11, upon sublimation, gave colorless crystals at 130 "C which were characterized to be {(Mefi)2b-OOC(Et2N)]2}: yield 20%; IH NMR (c6D6)6 -0.25 (s, 12H, Al(CH3)), -0.741 (t, 8H, CHzCHs), 2.81 (m, 12H, NCHzCH3); 13CNMR (C6Ds) 6 -10.75 (broad, Al(CH&), 12.45 (NCHzCHs),42.15 (NCH~CHS), 158.22 (oca); "A1 NhlR (C6D6) 140 (broad); IR 2911 (m), 1571 (s, br), 1494 (s), 1357 (s), 1201 (s), 1152 (s). Anal. Calcd: C, 47.88; H, 8.56; N, 9.31. Found: C, 47.56; H, 8.42; N, 9.05. Structure Determination. Crystals for X-ray measurements were sealed in glass capillaries. Preliminary examinations and intensity data collections were carried out with a Rigaku AFC6S or AFC7S diffractometer using graphiteI 1.541 78 & or Mo Ka (A = monochromatized Cu Ka (,= 0.710 69 8)radiation. Intensity data were collected using the 19-28 scan mode and corrected for absorption and decay. All structures were solved by SIR9229and refined with full-matrix least squares on F. In the final cycles all non-hydrogen atoms were refined anisotropically and all hydrogen atoms were fixed at idealized positions. All calculations were carried out with

a SGI R4000 computer using the teXsan program package.30 A summary of the data collection and structure solution is given in Table 1, and final atomic coordinates are given in Table 2.

Acknowledgment. Financial assistance from the National Science Council, Taiwan, ROC, is gratefully acknowledged. Supporting Information Available: Tables of crystal data, atomic coordinates and temperature factors, and intramolecular bond distances and angles of 1-6,9,and 10 and figures giving additional views of 2 and 4 (111 pages). Ordering information is given on any current masthead page. OM9502547 (29) SIR92: Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, M.; Giacovazzo, C.; Guagliardi, A,; Polidori, G. J.Appl. Crystallogr. 1994, 27, 1045. (30) teXsan: Crystal Structure Analysis' Package; Molecular Structure Corp.: College Station, TX, 1985, 1992.