Butatrienylidene Complexes

The reactions of various butatrienylidene complexes with water [14, 19, 20, 48] giving acylethynyl complexes very likely proceed by initial attack of water (or OH ) at C3 of the butatrienylidene ligand. 

The reaction of aromatic imines with [Cp(PPh3)2Ru=C=C=C=CH2] gave two types of products, either l-azabuta-l,3-diene-2-ethynyl complexes or 4-ethynylquino-line complexes [52, 53]. The azabutadiene-2-ethynyl complexes were thought to be 

Anionic nucleophiles such as I, OH, N3, or CH3 did not add to C3 of the butatrienylidene ligand of 11 but rather replaced the trans chloro ligand. When the trans hydroxo butatrienylidene 28 was treated with PhOH, instead of an allenylidene complex (3,4 addition produd) or an alkenylvinylidene complex (2,3 addition 

The LUMO in d pentatetraenylidene complexes is predominantly localized on the odd carbon atoms and to a lesser extent on the metal. The coefficients on Cl and C3 are very similar, independent of the metal-ligand fragment and the terminal substituent. The coefficient at C5 is somewhat larger. In square-planar d rhodium and iridium complexes the coefficient at the metal is comparable to that on C5 and is larger than those on Cl and C3. Thus, a nucleophilic attack at the metal of d complexes has also to be taken into account. 

However, alcohols or secondary amines usually add to the C3=C4 bond of pentatetraenylidene complexes of mthenium generated in situ and the finally isolated products are the corresponding alkenylallenylidene complexes. 

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The majority of butatrienylidene complexes synthesized or generated so far were obtained by following route a and using butadiyne or a butadiyne derivative as the source of the C4 fragment. A few complexes of iridium or manganese were synthesized by the substitution route c. Until now route b has not been (successfijlly) employed. 

The first butatrienylidene complexes were generated by Bruce et al. [14] and Lomprey and Selegue [15, 16[ in 1993. 

The first isolable, albeit binuclear, butatrienylidene complexes, the cationic diiron complexes 8, were likewise prepared by addition of an electrophile E+ to neutral butadiynyl complexes. Instead of mononuclear butadiynyl complexes, binuclear C4-bridged butadiyndiyl complexes 7 were used as the starting complexes by Lapinte et al. (Scheme 3.4) [18]. Complexes 8 were characterized by multinuclear NMR, IR, UV-vis, and Mossbauer spectroscopies, mass spectrometry and cyclic voltammetry. 

Scheme 3.4 Synthesis of the first binuclear butatrienylidene complexes by addition of electrophiles to butadiyndiyi diiron...

An alternative route to cationic butatrienylidene complex 4 involves 1,4-H shift in butadiyne complex 9. The formation of 4 as an intermediate in the reaction of [Cp(PPh3)3Ru-Cl] with AgPFg and buta-l,3-diyne was deduced from trapping experiments. Complex 4 thus generated gave with diphenylamine the corresponding diphenylamino(methyl)allenylidene complex (Scheme 3.5) [19]. 

Scheme 3.6 Formation of the butatrienylidene complex 10 by reaction of [RuCl2(dppm)2] with butadiyne.

Rearrangement reactions have turned out to be very convenient and the most used methods for the synthesis of butatrienylidene complexes. 1,4-H shift reactions have been used by Bruce et al. [19, 20] and Winter et al. (e.g.. Scheme 3.6) [21, 22] for generating butatrienylidene ruthenium complexes. Analogously, a butatrienylidene iron complex tvas obtained from [Cp (dppe)Fe-Cl] (dppe = Ph2PCH2CH2PPh2), Mc3Si-C = CC = CH, and NaBPh4 in methanol via 1,4-H shift (Scheme 3.7) [23, 24]. 

Scheme 3.8 Synthesis of the first isolable neutral butatrienylidene complex.

Recently, isolable bis (triphenylstannyl)-substituted butatrienylidene complexes of manganese (13) were obtained by photolysis of alkynyl(triphenylstannyl)vinylidene complexes 12 (Scheme 3.9) [4, 5]. Treatment of the resulting bis(stannyl)butatrie-nylidene complexes 13 with tetrabutylammonium fluoride and water afforded the first characterizable butatrienylidene complexes (14) containing an unsubstituted [M=C=C=C=CH2] moiety (Scheme 3.9). In contrast to 13, complexes 14 were unstable above —5 °C and were therefore characterized in solution only by NMR spectroscopy at —40°C. Complexes 14 were also formed instantaneously when solutions of 12 were treated at — 30 °C with one equivalent of tetrabutylammonium fluoride. 

A bis(trimethylstannyl)-substituted butatrienylidene complex (17) related to 13 (R = R = Me) was formed in the reaction of cydoheptatrienyl(methylcyclopentadie-nyl)manganese with Me3SnC = C-C = CSnMc3 and dmpe. Complex 17 was obtained... 

Allyl amines, allyl thioethers, and allylferrocenylselenide react analogously with butatrienylidene complex 10 by initial addition to C3 and subsequent hetero-Cope or hetero-Claisen rearrangement (Scheme 3.23) [21, 42-45]. 

Scheme 3.26 Formation of azabutadiene-2-ethynyl complexes in the reaction of butatrienylidene complexes with imines.

The reactivity of d butatrienylidene complexes towards simple electrophiles is rather unexplored. The manganese complexes [(C5H4R)(P-P)Mn=C=C=C=C (SnPh3)2[ (R=H, Me P-P = dmpe, depe) were found to react ivith [NBu4]F/H20 to give the unsubstituted butatrienylidene complexes [(C5H4R)(P-P) Mn=C=C=C=CH2] (see Scheme 3.9) [4, 5]. 

The reactivity of neutral square-planar d butatrienylidene complex 11 (Scheme 3.8) strongly deviates from that of cationic d ruthenium complexes. The deviation is readily understood when considering the orbital contributions of the metal and the carbon atoms of the chain to the LUMO. In d and d complexes the LUMO is predominantly localized at the metal, at Cl and C3. However, the relative contribution of the metal in d and d complexes is significantly different. In d complexes the metal contributes considerably less than Cl and C3, in d complexes its contribution is approximately equal to that of Cl and C3. 

The reactions of butatrienylidene iridium complexes with CO depend strongly on the trans ligand. The trans chloro complex 11 reversibly adds CO to form a five-coordinate butatrienylidene complex 31 whereas the trans azido complex yields with CO an alkenyl(azido)ethynyl complex (32) and the trans methyl complex the alky-nylalkenyl complex 33 (Scheme 3.31) [3]. 

The complexes Cp (PP)Fe ( i-C=CC=C) Fe(CO)2Cp (PP = dppe 100, dippe 102) are protonated (HBF4Et20) or methylated (MeOTf) to give [ Cp (PP)Fe i-C=C=C=CR[Fe(CO)2Cp ] ]BF4 (190a-d) (R = H, Me), which can be isolated as moderately stable powders (Scheme 43). The UV-vis spectra of these deep purple butatrienylidene complexes have characteristic absorptions between 527 and 546 nm (s ca. 15,000).259 The absence of v(CC) bands between 1500 and 1650 cm-1 excludes the ethynylvinylidene formulation, and bands at 1952, 1776 (dppe/H), 1945 (dippe/H), 1942, 1882, 1830 (dppe/Me), and 1946 cm-1 (dippe/Me) were tentatively assigned to v(CC) modes. In 13C NMR spectra, resonances beween 250 and 265 ppm [2/(CP) ca. 35 Hz] were assigned to the carbon adjacent the Fe(PP)Cp moiety. The other carbon resonances were assigned on the basis of /(CH) and the assumption that the chemical shifts will move upfield along the chain. The Mossbauer spectra contained two quadrupole doublets, with 5 values similar to those shown by Fp Me or allenylidene... 

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