The (alkynylcarbyne)tungsten complexes [L 3 (CO) 2 W C C C R] (3a,b-6a,b) [L 3 = hydro[tris(3,5-dimethylpyrazol-1-yl)]borato (Tp%, 3), hydro[tris(pyrazol-1-yl)]borato (Tp, 4), cyclopentadienyl (Cp, 5), bis(3,5-dimethylpyrazol-1-yl)acetato (bdmpza, 6); R =SiMe 3 (a), Ph (b)] were prepared in a stepwise fashion from [W(CO) 6 ] and Li[C CR], (CF 3 CO) 2 O and M[L 3 ] (M=Na, K). The formation of 6a,b was highly selective, only complexes with a trans arrangement of the carboxylate group of bdmpza and the alkynylcarbyne ligand were detected. The reaction of [W(CO) 6 ] with Li[C CR], C 2 O 2 Cl 2 and tmeda afforded trans-[Cl(CO) 2 (tmeda)W C C C R] (7a,b). The electron-donating potential of the different tripodal ligands L 3 was studied by IR-and 13 C-NMR spectroscopy and compared to that of the ligand combination Cl/tmeda. The IR data suggest that in these complexes bdmpza is a weaker electron donor than Tp% and Tp but displays stronger electron-donating abilities than Cp. The structures of 6b and 7b were established by X-ray structural analyses.

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Pentacarbonyl(pentamethylenevinylidene)chromium, [(CO),Cr=C=C(CH,),] (l), reacts with l-methylthio-l-propyne (2a) and N-( 1-propyny1)phenothiazine (2b) by regiospecific addition of the C=C bond of the alkyne to the C=C bond of the vinylidene ligand of 1. Initially, complexes with a spirocyclic cyclobutenylidene ligand are formed, [(CO) Previously, we described the synthesis of n-donor-substituted cyclobutenylidene complexes and cyclobutenones from pentacarbonyl(viny1idene) complexes of chromium and tungsten and electron-rich alkynes such as l-diethylamino-and l-ethoxy-l-pr~pyne [~~]. We now report on the preparation of pentacarbonylchromium complexes with a spirocyclic cyclobutenylidene ligand, the thermal rearrangement of the cyclobutenylidene ligands to substituted 4,5,6,7-tetrahydroindenes and the decomplexation of N-(2-methyl-4,5,6,7-tetrahydroindenyl)phenothiazine. Results and DiscussionThe starting pentamethylenevinylidene complex (l)IZ4] was generated by the reaction sequence shown in Scheme 1. Reduction of Cr (C0) At O"C, complex 1 rapidly reacts with l-methylthio-lpropyne (2a) in n-pentaneldichloromethane to give the 2-methyl-4,5,6,7-tetrahydroindenyl(methyl)thioether complex 4. Complex 4 is presumably formed by an initial regiospecific cycloaddition of the C=C bond of 2a to the C=C bond of 1 and subsequent ring expansion of the resulting 3-methylthio-substituted cyclobutenylidene complex 3 (vide infra) (Scheme 2). [2 + 21 cycloaddition of alkynes to the C=C bond of pentacarbonyl(viny1idene) complexes was also observed in the reactions of ynamines and alkoxypropynes with (C0)5M=C=CR2 (M = Cr, W R = alkyl,

Thermolysis of the pentacarbonyl(vinylidene)chromium complexes [(CO) 5 CrÄ/CÄ/C(R 1)R 2 ] (1a Á/d) (C(R 1)R 2 0/CMe 2 (a), C(CH 2) 5 (b), C(Et)Me (c), C(t Bu)Me (d)), affords binuclear, vinylidene-bridged nonacarbonyldichromium complexes, [(CO) 5 Cr(m-h 1 ,h 2-CÄ/C(R 1)R 2)Cr(CO) 4 ] (2a Á/d). The solid-state structures of 2a and 2d have been established by X-ray structural analyses. The structural data prove the m-h 1 ,h 2-C Ä/C(R 1)R 2 bonding mode. To account for the NMR spectroscopic features a dynamic process is proposed involving rapid coordination site exchange of the CÄ/C bond between Cr(1) and Cr(2) (windshield wiper mechanism) and of one CO ligand.

Aminolysis of 3-alkoxycyclobutenylidene complexes offers a convienient and high-yield route to a variety of 3-aminocyclobutenylidene complexes. Thus, the 3-diethylaminocyclobutenylidene complexes [(CO) 5 Cr C(C(Me) C(NEt 2) Ç ¹¹¹¹¹¹¹¹¹¹¹º R 2)] [(4), R 2 (CH 2) 5 (a), Me 2 (b), Ph 2 (c)] are obtained by substitution of NEt 2 of diethylamine for the ethoxy group in [(CO) 5 Cr C(C(Me)C(OEt) Ç ¹¹¹¹¹¹¹¹¹º R 2)] (3a-c). The reactions of (R) N-methyl-1-phenylethyl amine and of (S)-2-methoxymethylpyrrolidine with 3a-c afford the 3-N-methyl-(1-phenylethyl)amino-and 3-(2-methoxymethyl-pyrrolidino)-substituted cyclobutenylidene complexes, respectively, as mixtures of the E and Z isomers (with respect to the C3 N bond). Mixtures of the E and Z isomers of 3-(amino acid ester)-substituted cyclobutenylidene complexes are obtained from 3a,b and the methylester of L-leucine, L-phenylalanine, and L-methionine in yields ranging from 82 to 94%. The E/Z ratio strongly depends on the amino acid and the substituents at the sp 3-C atom of the cyclobutenylidene ring. The reactions of 3a-c with cysteine, H 2 N C 2 H 4 SH, proceed highly selectively. Only 3-aminocyclobutenylidene complexes are isolated in 73-86% yield. The formation of 3-organylthiocyclobutenylidene complexes has not been detected. The structure of the E-leucinyl methylester-substituted complex has been established by an X-ray structural analysis.