Lidmila Petrusová

Titanium-catalyzed head-to-tail dimerization of tert-butylacetylene. Crystal structures of [(C5HMe4)2Ti(μ-H)2Mg(THF)(μ-Cl)]2 (THF-tetrahydrofuran) and (C5HMe4)2TiOCMe3

Abstract tert-Butylacetylene (TBUA) is readily dimerized exclusively to 2,4-di-tert-butyl-1-buten-3-yne, head-to-tail dimer (HTTD), in the presence of the (η5-C5HMe4)2TiCl2/Mg/THF system. The ESR investigation revealed the formation of Ti–Mg hydride complexes [(η5-C5HMe4)2Ti(μ-H)2Mg(THF)(μ-Cl)]2 (2) and [(η5-C5HMe4)2Ti(μ-H)2]2Mg (3) in the absence of TBUA and a tweezer-type complex, probably [(η5-C5HMe4)2Ti(η1-CCCMe3)2]− [Mg(THF)Cl]+ (4) in its presence. The catalytic system as well as complexes 2–4 were deactivated by presumably tert-butanol contained in TBUA to give (η5-C5HMe4)2TiOCMe3 (5). Purification of TBUA improved the turnover by up to 8.8×103 mol TBUA per 1 mol Ti using complex 3 as a catalyst, however, complex 5 remained the only observable product of deactivation. The crystal structures of 2 and 5 were determined by X-ray diffraction analysis.

Permethyltitanocene-bis(trimethylsilyl) acetylene, an efficient catalyst for the head-to-tail dimerization of 1-alkynes

Abstract In the series of the (C 5 H 5− n Me n ) 2 Ti[ η 2 -C 2 (SiMe 3 ) 2 ] ( n = 0−5) ( 1A–1F ) complexes only (C 5 Me 5 ) 2 Ti[ η 2 -C 2 (SiMe 3 ) 2 ] ( 1F ) catalyzed the linear head-to-tail dimerization of 1-alkynes. A selectivity of better than 98% and a turnover number ( TN ) in the range 1200–1500 mmol of 1-alkyne per mmol of Ti was obtained after 14 d at 30°C for 1-pentyne, 1-hexyne, cyclohexylethyne, phenylethyne and trimethysilylethyne. Among other complexes in the series, 1A–1D attained TN ⩽ 25 after 5 d at 30°C and produced mainly a mixture of 1,3,5- and 1,2,4-trisubstituted benzene derivatives. The complex (C 5 HMe 4 ) 2 Ti[ η 2 -C 2 (SiMe 3 ) 2 ] ( 1E ) afforded ca. 20% of the head-to-tail dimers in addition to cyclotrimers but its activity was extremely low, corresponding to TN ∼ 7. The rate of dimerization by 1F is controlled by slow exchange rate of 1-alkynes with bis(trimethylsilyl)acetylene.

Formation of a binuclear titanocene hydride–magnesium hydride carbyl-bridged complex in the (C5Me4Ph)2TiCl2/Mg/THF system

Abstract The reduction of (C5Me4Ph)2TiCl2 by magnesium in tetrahydrofuran affords a mixture of the diamagnetic doubly tucked-in titanocene complex (C5Me4Ph)[C5Me2(CH2)2Ph]Ti (1), the paramagnetic trinuclear Ti–Mg–Ti hydride bridged complex [(C5Me4Ph)2Ti(μ-H)2]2Mg (2) and the paramagnetic binuclear titanocene hydride–magnesium hydride complex (C5Me4Ph)[C5Me4(o-C6H4)]Ti(μ-H)2Mg(THF)2 (3). The X-ray diffraction analysis of 3 revealed that the magnesium atom forms the σ-bond to the ortho-carbon atom of one of the phenyl rings and binds 2 molecules of THF.

Fermethyltitanocene(III) diacetylide - magnesium tweezer complexes, intermediates in the catalysis of linear head-to-tail dimerization of terminal acetylenes

The (C5Me5)2TiCl2/i-PrMgCl/Et2O (Mg:Ti  4–10) catalytic systems selectively catalyze the dimerization of terminal acetylenes RCCH to 2,4-disubstituted 1-buten-3-ynes for R  Me, Et, n-Pr, n-Bu, cyclohexyl, Ph, and SiMe3 with a turnover number 500–700 after 5 days. The ESR investigation of these systems has revealed that permethyltitanocene tweezer complexes with embedded Mg ion between the acetylene arms [(C5Me5)2Ti(η1-CCR)2]−[Mg(OEt2)X]+ (XCl or CCR) (1A–1G for R  Me, Et, n-Pr, n-Bu, cyclohexyl, Ph, and SiMe3) are intermediates in the formation of a dimerization catalytic center. Their ESR spectra are characterized by g-values in the range 1.990–1.993, coupling constant to the proton at α-carbon atom of the acetylene substituent 2.0–2.5 G and by coupling constants to 47Ti and 49Ti isotopes in the range 7.6–8.7 G. The tweezer complex [(C5Me5)2Ti(η1-CCSiMe3)2]−[Mg (THF)Cl]+ (2G) has been synthesized. It catalyzes the head-to-tail dimerizations with the same selectivity and similar turnover numbers as the above systems.

Synthesis of {1,3-bis(η5-tetramethylcyclopentadienyl)-1,1,3,3-tetramethyldisiloxane}dichlorotitanium(IV) via hydrolysis of bis{η5-(N,N-dimethylaminodimethylsilyl)tetramethylcyclopentadienyl}dichlorotitanium(IV)

Abstract Bis{η5-(N,N-dimethylaminodimethylsilyl)tetramethylcyclopentadienyl}dichlorotitanium(IV), [TiCl2{η5-C5Me4(SiMe2NMe2)}2] (1), easily undergoes hydrolytic cleavage of the Si–N bonds to give dimethylamine and {1,3-bis(η5-tetramethylcyclopentadienyl)-1,1,3,3-tetramethyldisiloxane}dichlorotitanium(IV), ansa-[TiCl2{(η5-C5Me4SiMe2)2O}] (2), in almost quantitative yields. The crystal structures of compounds 1 and 2 were determined by single-crystal X-ray diffraction.

Cometathesis of dicyclopentadiene with esters of unsaturated carboxylic acids by high valent tungsten chlorides as unicomponent catalysts

Abstract Activity of WCl 6 , WCl 5 (OAr) and WOCl 4 as unicomponent catalysts was studied in metathesis of unsaturated esters. WCl 6 , and WCl 5 (OAr), where Ar= p -chlorophenyl and p - t -butylphenyl were found to be active in ring opening metathesis of 5-norbornene-2-yl acetate (NBEAc) and in copolymerization of NBEAc with dicyclopentadiene (DCPD). Completely soluble copolymers were prepared in the latter case and copolymerization parameters r 1 = r 2 =1 were found. Cometathesis of DCPD with methyl undecenoate and dimethyl 3-hexenedioate leads to the formation of low molecular weight polymer and/or oligomers containing 1 or 2 ester groups in the molecule. Effects of ester groups on catalytic activity of WCl 6 in DCPD polymerization was studied using definite additions of methyl palmitate (MP). With increasing amounts of MP, reduction of polymerization rate and, significantly, growth of the non-crosslinked polymer fraction occur. Although hydrocarbons with highly strained norbornene ring are necessary for the formation of catalytic active centres, catalytic activity of centres already formed is not restricted on the substrates with such a ring. However, their reactivity depends on the ring strain considerably and this substrate selectivity still increases in the presence of esters.