Square planar geometry distorted

Its structure shows the trans-influence of hydride and pronounced distortion from square planar geometry (H—Rh-P 70.7°) owing to steric crowding. (RhH(PPh3)3 is rather less distorted (H-Rh-P 75.8°) [118a], This 16-electron complex shows no tendency to add an extra molecule of phosphine, unlike the less hindered RhH(PEt3)3. It is, however, an active... 

The cation has significant tetrahedral distortion from square planar geometry (P—Ir—P 150°) to minimize non-bonding interactions. It undergoes various oxidative addition reactions... 

The similar species Ir(PMe3)4 likewise shows tetrahedral distortion from square planar geometry (P-Ir—P 152.6-158.9°). It undergoes some remarkable oxidative addition reactions with species like H2O and H2S (Figure 2.72). 

Various mixed tridentate ligands with P,N,0/S/N donor sets have been explored in Ni11 chemistry. For example, condensation of 2-(diphenylphosphino)aniline with substituted (5-chloro-, 5-nitro, 5-bromo-, 5-methoxy-, and 3-methoxy-) salicylaldehydes yields (253).697 The deprotonated ligand coordinates through its P,N,0 donor set in a square planar geometry with some distortion, which is probably due to the bulk of the phosphine group and to the bite angle of the P,N chelate. 

With P-donors a variety of different structures are formed. Two complexes (359a,b) with a five-coordinate square pyramidal geometry and one S-donor in the apical position are reported.934,933 In a related complex (360) the nickel center reveals a distorted square planar geometry, because one xanthate ligand switched to a monodentate coordination mode. 6 By reaction of [NiL2] complexes with Ph2P(CH2)2P(Ph)(CH2)2PPh2, compound (362) is formed, which consists of a five-coordinate cation and a hexacoordinate anion. 7... 

The [Pt(Se4)2]2 complex (133) has been prepared by the reduction of the platinum(IV) species [Pt(Se4)3]2 with excess borohydride.328 The X-ray structure of the complex shows that each of the five-membered rings adopts a half-chair conformation, with the platinum coordination sphere exhibiting slight distortion from a square-planar geometry.329... 

Lippard characterized the structural effect of variation in the alkyl bridge length in tropocoro-nand complexes of zinc (80). Six complexes of ligands with bridge lengths from n = m = 3 to n = m = 6 were structurally characterized.702 The complexes had distorted tetrahedral-square planar geometries, with the exception of the m = n = 3 adduct which was five-coordinate with an additional pyridine ligand. 

Structures have been determined for PR3 = PMe2Ph and PBu3 [61]. In the former, the square planar geometry is retained (with slightly shorter Rh-P bonds (2.316 A) than for PR3 = PPh3), but in the latter, there is pronounced lengthening of the Rh—P bonds (Rh—Cl 2.395 A, Rh—P 2.425-2.430 A, Rh-C 1.784 A) and a distortion towards a tetrahedral structure (P-Rh—P... 

Andrus et al. (109) proposed a stereochemical rationale for the observed selec-tivities in this reaction. The model is based on the Beckwith modification (97) of the Kochi mechanism, suggesting that the stereochemistry-determining event is the ally lie transposition from Cu(III) allyl benzoate intermediates 152 and 153, Fig. 13. Andrus suggests that the key Cu(III) intermediate assumes a distorted square-planar geometry. Steric interactions are decreased between the ligand substituent and the cyclohexenyl group in Complex 152 as opposed to Complex 153 leading to the observed absolute stereochemistry. 

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