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The novel tridentate ligand in 1 was generated by head‐to‐head coupling and double insertion of PhC≡CH into the Rh−O bond of [(η5‐C5Me5)RhCl{PPh2(2‐O‐6‐MeOC6H3)}]. Propargylic esters (Me, Et) undergo single insertion to give seven‐membered metallacycles.

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A new series of N 2 O tridentate ligands HL n (n ) 2-5) have been prepared through N-methylation or N-benzylation of 2-N-(2-pyridylmethyl)aminophenol (HL 1 ). Treatment of these ligands with WO 2 Cl 2 (DME) (DME ) 1,2-dimethoxyethane) in the presence of triethylamine leads to the formation of cis-dioxotungsten(VI) complexes WO 2 (L n )Cl (n ) 1-5). Reaction of WO 2 (L 1 )Cl with Me 3 SiCH 2 MgCl gives the alkyl derivative WO 2 (L 1 )-(CH 2 SiMe 3 ), which has been structurally characterized.

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Metal alkynyl complexes are currently of great interest [1,2] since they are valuable for constructing vinylidene or carbene complexes for use in organic synthesis. [3±8] Reactions of organotransition metal halides with 1-alkynes in the presence of anions such as PF 6 À , BF 4 À , and CF 3 SO 3 À are representative methods for the preparation of vinylidene complexes. [9] One ortho-methoxy group in (2,6-dimethoxyphenyl)diphenylphosphane (mdmpp) was demethylated in the reaction with the isoelectronic complexes [(h 6 -arene)RuCl 2 ] 2 (arene C 6 Me 6 , p-cymene, C 6 H 3 Me 3 ) and [Cp*MCl 2 ] 2 (M Rh, Ir) to give metal complexes with a (P,O)-chelating phosphane: [(h 6arene)RuCl(mdmpp-kP,kO)] [10,11] and [Cp*MCl(mdmpp-kP,kO)] [12,13] (Cp* C 5 Me 5 ). We recently reported the unprecedented insertion of tetracyanoethylene (tcne) and tetracyanoquinodimethane into the CÀH bond adjacent to the MÀO bonds of the above rhodium(iii) and iridium(iii) complexes to produce (Pin the case of tcne. [14] Treatment of the ruthenium(iii) complex with PhCCH in the presence of NaPF 6 in acetone/CH 2 Cl 2 afforded the vinylidene complex [(h 6 -arene)Ru(mdmpp-kP,kO)( C CHPh)]-PF 6 . [15] However, treatment of [Cp*RhCl(mdmpp-kP,kO)] (1) [12] with 1-alkynes such as HCCCOOMe, PhCCH, and nBuCCH, and the disubstituted alkyne C 2 (CO 2 Et) 2 in the presence of NaPF 6 or KPF 6 resulted in unusual reactions (Scheme 1). In the reaction with HCCCOOMe, extraction of CO from the ester group of one and insertion of another 1-alkyne molecule into the RhÀO s bond occurred to produce a seven-membered metallacycle, and reactions with HC CR led to the formation of complexes with five-and six-membered rings by double insertion of 1-alkynes into the RhÀO bond. The disubstituted alkyne also underwent single insertion into the RhÀO bond. Similar insertion of unsaturated molecules into the metal ± oxygen bonds of metal alkoxides was achieved with cyclooctadiene [16] and perfluoroolefins [17] such as F 2 CCF 2 and hexafluorocyclobutene. The insertion of alkynes into the transition metal to oxygen s bonds was achieved here for the first time. [18] Interestingly, these unprecedented reactions allow single and double insertion of alkynes into the RhÀO bond of 1 to be controlled by means of the alkyne substituents. Experimental SectionThe reactions were carried out with the same batch of catalyst in the absence of oxygen and water under the following conditions: (SiO) 2 TaÀH (prepared by impregnation, 18.8  10 À6 mol of Ta, 1 equiv), alkane (40 Torr, 43 equiv), and H 2 (630 Torr, 710 equiv) were heated with an oil bath to the desired temperature (AE 1 8C) in a glass batch reactor (376 mL). During the reaction, aliquots were expended, brought to atmospheric pressure, and analyzed by gas chromatography (HP 5890 apparatus, Al 2 O 3 / KCl on fused silica column, 50m  0.32mm). Alkanes and H 2 were dried over freshly regenerated molecular sieves (3) and deoxo traps before addition.[1] For the low-temperature hydrogenolysis of alkanes on group IV silica supported comple...