Reactions trigonal-bipyramidal complexes

Dioxygen and its ions can bind in mononuclear and dinuclear structures in a number of ways,962 as illustrated in Scheme 1. The typical reaction of dioxygen with Co compounds involves a number of these binding forms, outlined in Scheme 2. Mononuclear Co111—peroxo complexes are relatively rare, but yellow trigonal bipyramidal complexes [Co(02)L2]+ (L = chelating phosphines dppe or dppp) have been characterized structurally where the 022 is bonded to the Co in the side-on r]2 form (Co—O 1.858(7) 1.881(4) A), with O—O stretching frequencies ( 870 cm-1) consistent with Coin-peroxo speciation.963... 

A further reaction of [Ir(cod)Cl]2 with 3,4-dimethylphosphaferrocene, (355), yields the trigonal-bipyramidal complex [Ir(355)3(cod)]BF4, (356). 79 (356) reacts with H2 under pressure to give [Ir(355)4H2]+. Reaction of Ir(cod)Cl]2 with o-diphenylphosphinobenzoic acid ethyl ester (dpes), (357), yields [IrCl(cod)(dpes)], where dpes is acting as a monodentate P-donor-atom ligand.580 When dpes is reacted with [Ir(cod)2]BF4, then the structurally determined... 

Rana and Teotia 116) have reported the synthesis of a novel tridentate macrocycle 136 by the reaction of 2,6-dipicolinic acid hydrazide and acetylacetone in the presence of cobalt(II), nickel(II), and copper(II) salts. As is frequently the case, water occupies the axial positions of these trigonal bipyramidal complexes and the chelating nitrogen atoms are essentially coplanar. 

The reaction of tra 3 -IrCl(CO)(PPh3)2 with carbon disulfide in the presence of NaBPli4 yields [(49)](BPli4) in which the S-donor ligand is the zwitterion S2C PPh3+. Sulfur dioxide is S-bonded to an iridium(I) atom in the trigonal bipyramidal complex IrH(PPh3)2(CO)(S02) in the related chloro complex (50), the Ir-S distance is 2.45 A. ... 

Reactions of 16-electron intermediates with ligands occur very rapidly by an associative reaction. These reactions will be covered in Section 3.1 on dissociation from 18-electron complexes. Evidence for the trigonal bipyramidal complex as an intermediate and for the preference of itt-acceptor ligands for the eqnatorial positions in this geometry comes from the work of Wing and Rettig. A stable trigonal bipyramidal trisolefin complex of Pt(ll) with all three olefins in the equatorial positions was isolated by... 

Type III. In this category of reaction, metal valence electrons are moved into energetically preferred spatial configurations with respect to the nonreacting ligands. An example is the transformation of the trigonal bipyramid complex 45 to 46. This process is similar to Type II transformations in that... 

Continuing this line of argument, we find that the predominance of trigonal-bipyramidal complexes of rhodium(I) and iridium(I) could well mean that Fig. 2, the traditional reaction profile, applies to the little-studied ligand-exchange reactions of 4-coordinate complexes of these elements. However, such conclusions, unsupported by other evidence, must remain tentative,... 

A.iii. Sodium Tetracarbonyl Ferrate. An extremely useful organoiron reagent is sodium tetra-carbonyl ferrate [Na2Fe(CO)4], usually prepared by reduction of iron pentacarbonyl. The synthetic utility of this reagent lies in its ability to react with alkyl halides in a stepwise manner, including the reaction with two different alkyl halides, as reported independently by Cooke and by Collman and co-workers. - When sodium tetracarbonyl ferrate reacted with 1-bromooctane, a trigonal bipyramidal complex (715) was formed... 

Puddephatt etal. [41] have studied the C-H or C-C bond activation in the alkane complexes [PtMe(CH4)L2] or [PtMe(CHjCH3)L2] (L = NH3 or PH3) as well as the reductive elimination of methane or ethane from the five-coordinate model complexes [PtHMe2L2] or [PtMesLi], respectively, by carrying out extended Hiickel molecular orbital calculations and density functional theory. The oxidative addition and reductive elimination reactions occur by a concerted mechanism, probably with a pinched trigonal-bipyramidal complex on the... 

Nickel(II) phosphine complexes have been reported to he efficient catalysts in carbonylation reactions. To investigate this reaction mechanism, we have studied the reaction of CO on the related Ni(II) complexes NiX2(PMes)n (n = 2,3) and [NiX(PMes)m]BFj> (m = 3,4). Pentacoordinate carbonyl nickel(II) species (without reduction of Ni(II) to Ni(0)) were isolated (1) by direct substitution of PMcs by CO in the pentacoordinate complex and (2) by addition of CO on the trans square-planar tetracoordinate complex. These compounds are trigonal-bipyramidal complexes with CO in equatorial position. The Ni-CO distance (1.73 A) is the shortest reported Ni-CO distance. Since these carbonylation reactions can be viewed as substitution of an equatorial PMes by CO in a TBP, they can be related to the substitution reactions in square-planar d metal complexes. 

One can spot some cases for which little or no rearrangement is required, which would result in facile association reactions. This is the case for the high-spin d complexes with sawhorse structure, which have been discussed in a previous section association of one ligand to give a trigonal bipyramidal complex, or of two ligands to form an octahedral derivative. 

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