A selective dimerization reaction of 1,3-butadiene in the presence of 2-propanol to give 1,3,7-octatriene has been developed. By modification of palladium carbene catalysts an unexpected selectivity switch from the telomerization to the dimerization product occurred. In applying the 1,3-bis(2,6-diisopropylphenyl)-4,5-dimethyl-3H-imidazolidenylpalladium(0) complex 9, unprecedented catalyst efficiency (TON > 80 000 and TOF > 5000 h(-1)) has been obtained for this transformation. [reaction: see text]

The mixed-ligand complex [IrCl(C2H4)(SbiPr3)(PiPr3)] (2), prepared from [IrCl(C2H4)(PiPr3)]2 (1) and SbiPr3, reacts not only with CO, diphenylacetylene, and H2 by ligand substitution or oxidative addition but also with diaryldiazomethanes R2CN2 to give the four-coordinate iridium(I) carbenes [IrCl(CR2)(SbiPr3)(PiPr3)] (8−10) in 60−70% isolated yield. In contrast, treatment of 2 and of the related cyclooctene derivative trans-[IrCl(C8H14)(SbiPr3)2] (12) with C5Cl4N2 affords the diazoalkane complexes trans-[IrCl(N2C5Cl4)(SbiPr3)(EiPr3)] (11, E = P; 13, E = Sb) without elimination of N2. Displacement of the stibine ligand in 8−10 by PiPr3 leads to the corresponding bis(phosphine) compounds trans-[IrCl(CR2)(PiPr3)2] (14−16), while the reaction of 8 (R = C6H5) with NaC5H5 yields the half-sandwich-type complex [(η5-C5H5)Ir(CPh2)(PiPr3)] (17). Protonation of 17 with HCl occurs stepwise to give via the iridium(III) alkyl [(η5-C5H5)IrCl(CHPh2)(PiPr3)] (20) the ring-substituted isomer [(η5-C5H4CHPh2)IrHCl(PiPr3)] (21); however, if 17 is treated with HBF4, a cationic complex is formed which probably contains a η3-coordinated benzylic ligand. The square-planar iridium(I) carbenes 8 and 14 react with HBX4 (X = F, ArF) to afford the ionic products [IrHCl(CPh2)(PiPr3)(EiPr3)]BX4 (23, 24, E = P; 25, E = Sb) and with HCl to give the relatively labile octahedral species [IrHCl2(CPh2)(PiPr3)(EiPr3)] (26, E = P; 27, E = Sb). Treatment of 8 and 14 with ethene yields, besides [IrCl(C2H4)2(SbiPr3)2] (18) and/or trans-[IrCl(C2H4)(PiPr3)2] (28), a mixture of two isomeric olefinic products CH2CHCHPh2 (29) and CH3CHCPh2 (30), the ratio of which is independent of the ligand sphere of the iridium precursor. The molecular structures of 13, 14, 17, and 24 have been determined by X-ray crystallography.

Using the mixed phosphine−stibine compound [IrCl(C2H4)(PiPr3)(SbiPr3)] (2) as the starting material, the square-planar carbeneiridium(I) complexes [IrCl(CR2)(PiPr3)(SbiPr3)] (3a,b) and trans-[IrCl(CR2)(PiPr3)2] (4a,b) were prepared. The cyclopentadienyl derivative [C5H5Ir(CPh2)(PiPr3)] (5), obtained from 3a and NaC5H5, reacts with HCl by attack of the IrCPh2 bond; in contrast, upon treatment of 4a with HCl or HBF4, hydridoiridium(III) complexes 8 and 9 with an intact IrCPh2 unit are formed.

The reaction of [IrCl(C8H14)2]2 (2) with SbiPr3 in the presence of H2 yields the dihydridoiridium(III) complex cis,mer‐[IrH2Cl(SbiPr3)3] (3) which on treatment with CO and with HCCR (R = Ph, CO2Me) affords the octahedral derivatives [IrH2Cl(CO)(SbiPr3)2] (4) and [IrHCl(CCR)(SbiPr3)3] (5, 6), respectively. The stibane ligand trans to hydride in 5 and 6 is rather labile and, therefore, 5 and 6 react with pyridine to give [IrHCl(CCR)(py)(SbiPr3)2] (7, 8). Five‐coordinate bis‐(stibane)iridium(I) complexes [IrCl(C2H4)2(SbR3)2] (10–12) were prepared from [IrCl(C2H4)2]2 (9) and four equiv. of SbR3 (R = iPr, Me, Ph). The X‐ray crystal structural analysis of 10 reveals a distorted trigonal‐bipyramidal geometry around the metal center with one stibane ligand and the two olefinic ligands in the equatorial plane. Compound 10 reacts with NaC5H5 to yield [C5H5Ir(C2H4)(SbiPr3)] (13) and with different alkynes by partial or complete displacement of the ethene ligands to give trans‐[IrCl(PhCCPh)(SbiPr3)2] (14), [IrHCl(CCTol)(C2H4)(SbiPr3)2] (15), and trans‐[IrCl‐{CC(SiMe3)R}(SbiPr3)2] (16, 17), respectively.

Die Chloro‐verbrückte Iridium(I)‐Verbindung [Ir2(μ‐Cl)2(C8H14)4] (1) reagiert im Zweiphasensystem Benzol/Wasser mit KOH in Gegenwart von [NEt3(CH2Ph)]Cl (TEBA) zu dem entsprechenden Zweikernkomplex [Ir2(μ‐OH)2(C8H14)4] (2). Schrittweise Substitution der Cyclooctenliganden durch PiPr3 und Ethen führt in sehr guter Ausbeute über die Zwischenstufe [Ir2(μ‐OH)2(C8H14)2(PiPr3)2] (isoliert als Isomerengemisch 3 a, b) zu dem Produkt [Ir2(μ‐OH)2(C2H4)2(PiPr3)2] (4). Durch Reaktion von 4 mit PiPr3im Molverhältnis 1:2 entsteht die einkernige Verbindung trans‐[Ir(OH)(C2H4)(PiPr3)2] (5), deren Ethenligand bei Einwirkung von Ph2CN2 nicht durch CPh2 ersetzt werden kann.