The series of aryltris(2-propoxo)titanium reagents [ArTi(O-i-Pr) 3 ] 2 (Ar = Ph (1a), 2-MeC 6 H 4 (1b), 4-MeC 6 H 4 (1c), 4-ClC 6 H 4 (1d), 4-TMSC 6 H 4 (1e), 4-CF 3 C 6 H 4 (1f), 3,5-Me 2 C 6 H 3 (1g)) was synthesized from reactions of the in situ prepared ClTi(O-i-Pr) 3 with ArMgBr in THF. All compounds were characterized by NMR spectroscopy and elemental analyses. A variable-temperature 1 H NMR study of 1c suggested that compounds 1 are dimeric species in solution. The structures of complexes 1b,g were further determined by single-crystal X-ray analyses. X-ray diffraction studies confirmed that the aryltris(2propoxo)titanium complexes have a dimeric structure with a Ti 2 O 2 core bridging through the oxygen atom of two 2-propoxide groups. The application of aryltris(2-propoxo)titanium reagents to cross-coupling with aryl bromides catalyzed by the catalytic system of 1 mol % Pd(OAc) 2 and 2 mol % PCy 3 was studied. Results show that aryltris(2-propoxo)titanium compounds are excellent reagents for aryl-aryl coupling reactions at room temperature and that the system works well for a wide range of aryl bromides regardless of the electronic or steric nature of the substituents on the aryl bromides. Couplings with pyridyl bromides under the mild reaction condition of room temperature were also demonstrated to afford products in high yields over 2-3 h. It is worth noting that couplings with 3,3 0 -dibromo-2,2 0 -dimethoxy-1,1 0 -binaphthylene proceeded smoothly also at room temperature over 3-5 h, affording products in excellent yields. The coupling reactions demonstrated in this study are highly efficient compared to the typical synthesis of 3,3 0diaryl-2,2 0 -dimethoxy-1,1 0 -binaphthylenes via Suzuki couplings, which required higher catalyst loading under reaction conditions of longer reaction times (18-24 h in general) at elevated temperatures.

A novel asymmetric 3-furyl addition of (3-furyl)Ti(O(i)Pr)(3) to ketones in the presence of 10 mol % (S)-BINOL is reported. The catalytic system works excellently for aromatic ketones, alpha- or beta-halophenones, alpha,beta-unsaturated ketones, and acetylfuran, affording products in high yields with excellent enantioselectivities of up to 97% ee.

Highly efficient coupling reactions of benzylic bromides or chlorides with aryltitanium tris(isopropoxide) [ArTi(O-i-Pr)(3)] catalyzed by a simple palladium(II) acetate/tris(p-tolyl)phosphine [Pd(OAc)(2)/P(p-tolyl)(3)] system are reported. The coupling reactions proceed in general at room temperature employing low catalyst loadings of 0.02 to 0.2 mol%, affording coupling products in excellent yields of up to 99%. For benzylic bromides bearing strong electron-withdrawing cyano (CN) or trifluoromethyl (CF(3)) substituents, the reactions require a higher catalyst loading of 1 mol%, or the reactions are carried out at 60 degrees C. The catalytic system also tolerates (1-bromoethyl)benzene bearing beta-hydrogen atoms while using a catalyst loading of 1 mol% to afford the coupling product in a 70% yield

The synthesis of polyaryl phosphonium salts by cyclotrimerization of aryl alkynes is induced by a stoichiometric amount of the ruthenium η 5 -pentadienyl complex (η 5 -C 5 H 7 )(PPh 3 ) 2 RuCl (1). With only 1 mol % quantity, complex 1 efficiently catalyzed the dimerization of aryl alkynes at room temperature to afford the corresponding (Z)-1,4-diarylbut-1-en-3-yne derivatives as the major products. ■ INTRODUCTIONResearch over several decades on transition-metal pentadienyl compounds has revealed significant differences in the steric and electronic properties between the η 5 -pentadienyl (C 5 H 7 ) and η 5 -cyclopentadienyl (C 5 H 5 or Cp) ligands in transition-metal compounds. 1 The two ligands are isoelectronic; however, the C 5 H 7 ligand (cone angle 180°), 2 which is both a better δ backbonding acceptor and a better σ donor than the Cp ligand, 1 is also sterically more demanding than the Cp ligand (cone angle 145°). 3 Calculations predict that η 5 to η 3 conversions in the C 5 H 7 ligand should be easier than that in a C 5 H 5 ligand. 1 These differences among C 5 H 7 , Cp, and indenyl (C 9 H 7 ) ligands are expected to influence various properties of their compounds. The potential ring slippage from η 5 to η 3 in the C 5 H 7 ligand that may possibly create novel catalytic reactivity in ruthenium metal complexes has been investigated. 4 Dimerization of a terminal aryl alkyne catalyzed by [Ru]-Cl (1, [Ru] = (η 5 -C 5 H 7 )(PPh 3 ) 2 Ru) concomitantly giving an unidentified brown powder was disclosed in 2007. 5 Aiming at understanding the chemistry of ruthenium pentadienyl species derived from alkyne, we explore the reactions of arylacetylene with 1. In this paper, we report a practical and switchable reaction system using either a stoichiometric or a catalytic quantity of 1, leading either to the synthesis of polyaryl phosphonium salts via cyclotrimerization or to dimerization of aryl alkynes under mild condition, respectively. ■ RESULTS AND DISCUSSIONTrimerization. Treatment of phenylacetylene (2a) with a stoichiometric quantity of 1 affords no ruthenium acetylide or vinylidene complexes which are generally formed from the reaction of the corresponding (η 5 -C 5 H 5 )(PPh 3 ) 2 RuCl complex. Instead, the reaction of 2a with 1 and KPF 6 , both in stoichiometric quantities, gives a brown powder as the major product. The previously reported catalytic dimerization of 2a by 1 without any additive 5 revealed a similar brown powder which displayed a singlet resonance at δ 25.5 in the 31 P NMR spectrum in low yield and was not fully characterized. Our product formed in the presence of KPF 6 shows a slightly different resonance at δ 23.0 and displays a set of peaks at δ −150 attributed to PF 6 − . The previously reported complex is believed to have a chloride counterion, instead of PF 6 − , thus showing slightly different 31 P NMR data. 5 The structure of our brown powder has been fully characterized by a single-crystal X-ray diffraction analysis as the polyaryl phosphonium salt 6a, resulting from addition of PPh 3 to...

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Catalytic cyclization reactions and new stoichiometric skeletal rearrangement cycloisomerizations of 2‐ethynylphenyl vinyl ethers containing methyl substituents on the vinyl groups by using [Ru]Cl {[Ru]=Cp(PPh3)2Ru, Cp=η5‐cyclopentadienyl} were observed in MeOH and CH2Cl2, respectively. In MeOH, the catalytic cyclization of three different enynes gave the corresponding benzoxepine derivatives in high yields in each case. Interestingly, in the stoichiometric reactions of [Ru]Cl with enynes, two unprecedented rearrangements of enynes were observed in CH2Cl2. The presence of a methyl group in the vinyl unit plays a critical role in choosing one of the double bonds of the vinylidene ligand, that is, the Ru=Cα or the Cα=Cβ bond, for the [2+2] cycloaddition in the cycloisomerization processes. Structure determination by single‐crystal X‐ray diffraction analysis along with various isotope studies corroborated the proposed mechanisms.

In the title compound, [Al(C6H5)3(C4H8O)], the Al atom has a distorted tetra­hedral geometry. The C—Al—C angles range from 113.25 (7) to 116.27 (8)°, much larger than the O—Al—C angles, which range from 103.39 (7) to 103.90 (6)°. The tetra­hydro­furan ring adopts an envelope conformation. The crystal packing is stabilized by C—H⋯π inter­actions.

Cyclization of the ether enyne 1 catalyzed by [Ru]NCCH3(+) ([Ru] = Cp(PPh3)2Ru) in CHCl3 generates a diastereomeric mixture of the substituted tetrahydropyran 11. Presumably, formation of an allenylidene complex is followed by a cyclization by nucleophilic addition of the olefinic group to Cγ of the ligand giving a boat-like six-membered ring. The diastereoselectivity is controlled by the 1,3-diaxial interaction. The vinylidene complex 7, a precursor of 11, is obtained from 1 and [Ru]Cl. In a mixture of MeOH/CHCl3, the domino cyclization of 1 further affords 14a, a chromene product catalytically. The second cyclization proceeds via nucleophilic addition of the resulting olefinic unit to Cα of 7. But the ether enyne 3 with a cyclopentyl ring on the olefinic unit undergoes only single cyclization due to steric effect. The propargyl alcohol and the two terminal methyl groups on the olefinic unit shape the cyclization. Thus, similar all-carbon 1,n-enynes (n = 7, 8, 9) 4-6 each with an aromatic linker undergo direct domino cyclization catalyzed by [Ru]NCCH3(+), to give derivatives of tricyclic fluorene, phenanthrene and dibenzo[7]annulene, respectively, with no intermediate observed.