Tatsuya Makino

Publications (2)4.45 Total impact

• Article: Synthesis and Structure of Novel Iridium(I) Complexes Containing η4-1,6-Diene and Diphosphine Ligands:  Remarkable Effect of Ligand Bite Angle upon Ligand Dissociation

  Tatsuya Makino, Yoshihiko Yamamoto, Kenji Itoh
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  ABSTRACT: The treatment of [IrCl(cod)]2 with a bidentate diphosphine ligand, bis(diphenylphosphino)methane (dppm), and 1,6-dienes such as dimethyl 2,2-diallylmalonate (1) and diallyl ether (2) produces a ligand replacement reaction to afford novel iridium(I) complexes bearing η4-1,6-diene ligands, IrCl(dppm)[η4-CH2CHCH2C(CO2Me)2CH2CHCH2] (3) and IrCl(dppm)(η4-CH2CHCH2OCH2CHCH2) (4), respectively, in excellent yields. The molecular structure of the diallyl ether complex 4, which has been unequivocally determined by a single-crystal X-ray diffraction study, discloses that 2 coordinates to the iridium metal in an η4 fashion with a distorted-trigonal-bipyramidal geometry. In a similar manner, 1,2-bis(diphenylphosphino)ethane (dppe) is also a tolerant diphosphine ligand, and the corresponding η4-1,6-diene complexes IrCl(dppe)[η4-CH2CHCH2C(CO2Me)2CH2CHCH2] (5) and IrCl(dppe)(η4-CH2CHCH2OCH2CHCH2) (6) have been isolated in high yields. On the other hand, diphosphine ligands with a carbon linkage longer than that in dppe, such as 1,3-bis(diphenylphosphino)propane (dppp) and 1,4-bis(diphenylphosphino)butane (dppb), never activate the cod ligand, resulting in no exchange with the 1,6-dienes. Instead of the expected η4-1,6-diene complexes, IrCl(cod)(dppp) (7) and IrCl(cod)(dppb) (8) are exclusively formed. The molecular structure of 8 is also confirmed by an X-ray crystallographic analysis. The coordination geometry of 8 is consistent with a distorted square pyramid. The reactivity toward the ligand displacement depends on the natural bite angle of the bidentate phosphine ligands.
  03/2004;
• Article: Rhodium complex-catalyzed cycloisomerization of allenenes: exo and endo cyclization depending on the auxiliary ligands.

  Tatsuya Makino, Kenji Itoh
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  ABSTRACT: In the presence of a catalytic amount of a rhodium(I) complex, allenenes undergo cycloisomerization reactions resulting in the selective formation of exo-alkylidenecarbocycles and heterocycles. In the catalytic system of rhodium complexes with triaryl phosphites, cyclic 1,4- or 1,5-dienes are formed in good to excellent yields in the formal exo-cyclization mode via the metallacycle intermediate having an exo-alkylidene moiety. In this cycloisomerization, (E)- and (Z)-allenenes are transformed stereospecifically to the corresponding cyclic (E)- and (Z)-1,4-dienes, respectively. On the other hand, the reactions under carbon monoxide atmosphere exclusively afford seven-membered-ring products through an endo-mode cyclization. The unusual cyclization involves an allylic C-H activation process. The allenene bearing a silicon substituent at the olefinic terminus incorporates carbon monoxide to give the corresponding [2+2+1] cycloaddition product. This result apparently indicates that the catalysis of the rhodium complex is explained in terms of the oxidative cyclization of an allenene to furnish the key exo-alkylidene metallacycle intermediate at the first stage of the catalysis.
  The Journal of Organic Chemistry 02/2004; 69(2):395-405. · 4.45 Impact Factor