Frustrated and Realized Hydrogen Bonding in 4-Hydroxy-3,5-ditertbutylphenylphosphine Derivatives

Abstract

Synthesis and molecular and supramolecular structures of a series of triarylphosphines P(Ph) 3−n {4-RO-3,5-( t Bu) 2 -C 6 H 2 } n (n = 1, 3; R = SiMe 3 , H) are reported. Chemical oxidation products E=P(Ph) 3−n {4-RO-3,5-( t Bu) 2 -C 6 H 2 } n (E = O, S, and Se; n = 1, 3; R = SiMe 3 , H) are also reported. Crystal structures of the reported compounds were determined by single-crystal X-ray diffraction, using a Hirshfeld atom refinement with NoSpherA2 through OLEX2, which provides an average improvement in C−C bond distance precision of 35%. Phosphine basicity for the phosphines with n = 1, R = H and n = 3, R = SiMe 3 , H was determined using the 1 J P,Se values of the respective selenides; 1 J P,Se = 699 Hz for E = Se, n = 3, and X = H identifies the most basic triarylphosphine ever reported. Intermolecular interactions allow classification of the 17 structures into 4 categories: those with only dispersion-induced short contacts, those with frustration of H-bonding, those with only classic H-bonding, and those with combinations of classic and frustration of H-bonding. A "double phenol embrace" classified by an R 2 2 (4) graph set is a weak intermolecular synthon organizing lattices with 2,6-ditertbutylphenol functional groups. Classic H-bonding occurs only when E = O.

Accurate Crystal Structures of C12H9CN, C12H8(CN)2, and C16H11CN Valence Isomers Using Nonspherical Atomic Scattering Factors

“…Interestingly, and consistent with our previous experience applying HAR with NoSpherA2 on a series of organophosphine derivatives, 58 there is a strong trend in this improvement in All DFT calculations employed ORCA 5.0 using the PBE/def2-TZVP computational method. b All atoms were refined anisotropically, with the exception of 3 and 13, which implement disorder models.…”

“…The Z 3 -Csp 3 −H are in poorest agreement, while the number of determinations for Z 2 -Csp 3 −H is notably small. This study and our previous work 58 suggest a possible trend of somewhat shorter C−H distances than from neutron data over similar temperature ranges. There is no inherent reason for the two techniques to deliver the same values, but as demonstrated in Table 6, this HAR approach is 5− 15 times closer to the (neutron) reality than the fully constrained "riding-atom" model that is ubiquitously employed in the IAM.…”

“…This program uses custom atomic scattering factors that are fully polarized to the actual atom positions in the crystal lattice, which permits accurate placement of hydrogen atoms with a precision that approaches that of neutron diffraction, the acknowledged "gold standard" for light atom structures. 57 Our group has previous experience in the application of the HAR/NoSpherA2 method in the context of organophosphines 58 and copper(II) sulfates. 59 The impetus for adopting these HAR approaches is that standard resolution data from home labs equipped with area detectors often contain more information than the conventional independent atom model (IAM) can exploit.…”

“…Alternatively, the H-atoms could be positionally refined but with isotropic displacements. 58 The successful HAR/NoSpherA2 treatment of all 14 structures, with a sufficiently high data-to-parameter ratio to enable good-quality anisotropic displacement parameters of all ordered atoms, enabled accurate placement of H atoms. Only the H atoms in the minor components of the two-part disorder model of 13, and in the disordered and distorted molecule of 3, were refined isotropically and were also excluded from statistical comparisons.…”

“…The Z 3 -Csp 3 −H are in poorest agreement, while the number of determinations for Z 2 -Csp 3 −H is notably small. This study and our previous work58 suggest a possible trend of somewhat shorter C−H distances than from neutron data over similar temperature ranges. There is no inherent reason for the two techniques to deliver the same values, but as demonstrated in Table6, this HAR approach is 5− 15 times closer to the (neutron) reality than the fully constrained "riding-atom" model that is ubiquitously employed in the IAM.Analysis of C−H•••N�C Nonclassical H-Bonding and Dipolar C�N•••C�N Interactions in 2−14.Dunitz's skepticism about the significance of any interactions weaker than classical H-bonding113 has been resolutely countered by Lecomte et al114 by a consideration of the electron density distribution, and the Laplacian thereof, which affects all interatomic interactions, within and between molecules and ions.…”