Abstract
The crystal structures of tris-(3,5-di-methyl-phen-yl)phosphine (C24H27P), (I), tris-(3,5-di-methyl-phen-yl)phosphine oxide (C24H27OP), (II), tris-(4-meth-oxy-3,5-di-methyl-phen-yl)phosphine (C27H33O3P), (III), and tris-(4-meth-oxy-3,5-di-methyl-phen-yl)phosphine oxide (C27H33O4P), (IV), are reported. The strucure of (III) has been described before [Romain et al. (2000 ▸). Organometallics, 19, 2047-2050], but it is rereported here on the basis of modern area-detector data and to facilitate comparison with the other structures reported here. Compounds (I) and (II) crystallize isostructurally in P21/c. Similarly, (III) and (IV) crystallize isostructurally in Pbca. The conformations of (I) and (II) in the solid state deviate strongly from helical, whereas those of (III) and (IV) are found to be closer to an ideal threefold rotational symmetry. The pyramidality indices, ∑(C-P-C), are 305.35 (16), 317.23 (15), 307.2 (4) and 318.67 (18)° for (I), (II), (III) and (IV), respectively. Each is found to be more pyramidal than Ph3P or Ph3PO. Hybrid DFT calculations incorporating terms for dispersion provide evidence that the causes of the increased pyramidality, despite the 3,5-dimethyl group substitution, include dispersion inter-actions. The calculated ∑(C-P-C) values are 304.8° for both (I) and (III) and 317.4° for both (II) and (IV), with no difference arising from the substitution at ring position 4.
Highlights
That all these 3,5-dimethyl-substituted compounds should be more pyramidal than corresponding C6H5– derivatives is at first surprising
The preparation of (III) was reported by Romain et al (2000) some 11 years after it appeared in the patent literature
We report the crystal structures of (I), (II) and (IV) and full details for synthesis and characterization of (II) and (IV), for the first time, and the redetermination of (III)
Summary
The two bulky triarylphosphines (I) and (III) are of considerable interest in coordination chemistry and catalysis (Kakizoe et al, 2017; Lian et al, 2017; Ogiwara et al, 2017; Nishikawa et al, 2016; Naruto et al, 2015; Jover et al, 2010; Romain et al, 2000) and have been investigated for frustrated Lewis-pair activity (Wang & Stephan, 2014; Ullrich et al, 2010). The preparation of (III) was reported by Romain et al (2000) some 11 years after it appeared in the patent literature These authors reported a crystal structure, Cambridge Structural Database (CSD, Version 5.39, with updates to November 2017; Groom et al, 2016) refcode: FOQNOO. We report the crystal structures of (I), (II) and (IV) and full details for synthesis and characterization of (II) and (IV), for the first time, and the redetermination of (III) That all these 3,5-dimethyl-substituted compounds should be more pyramidal than corresponding C6H5– derivatives is at first surprising. The opPtimized geometries by DFT are characterized by common (C—P—C) = 304.8 for both (I) and (III) and 317.4 for both (II) and (IV) This supports dispersion as an origin for the observed increased pyramidality caused by 3,5-dimethyl group substi-
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