Stereochemical Alignment in Triphospha[3]ferrocenophanes

Abstract

A series of triphospha[3]ferrocenophanes of the type Fe(C5H4‐PtBu)2PX with X=H, F, Cl, Br, I, NEt2, tBu has been prepared and characterized by heteronuclear NMR spectroscopy and X‐ray crystallography. Despite having three stereogenic centers, the selective formation of a reduced number of diastereomers (either one or two) has been observed for these ferrocenophanes. Theoretical calculations revealed that the inversion of the central stereogenic center inverts the frontier orbital sequence leading to either an iron or a phosphorus centered HOMO depending on the respective diastereomer. CV measurements supported these results. For the all‐tert‐butyl substituted [3]ferrocenophane Fe(C5H4)2(PtBu)3 a chiral staggered conformation has been found in the solid state which differs substantially from the only other all‐organo substituted [3]ferrocenophane, Fe(C5H4)2(PPh)3.

Metallated [3]Ferrocenophanes Containing P3M Bridges (M = Li, Na, K) §

“…As a consequence of this steric effect, the torsion angle of the ferrocene unit slightly increased within the series, whereas the interplanar angle of the Cp rings decreased. Similar structural effects could be observed in triphospha [3]ferrocenophanes substituted with sterically demanding alkyl groups [10]. The M-P2 distances in 2-4 were all slightly below the sum of the Van-der-Waals radii [31].…”

“…Secondary triphosphane (1, Scheme 1) was obtained over the course of our investigations dealing with phosphorus-rich ferrocenophanes. It is stereochemically predefined in a way that only the optically inactive meso forms, cis and trans 1, are obtained, with the terminal bridgehead phosphorus atoms showing opposite absolute configuration, and both t-butyl groups pointing to the same side of the molecule [10]. Reaction of a diastereomeric mixture of cis and trans 1 with n-butyl lithium in hexane in the presence of tetramethyl ethylene diamine (TMEDA) afforded the envisaged lithium phosphanide (2, Scheme 1) in the form of a single diastereomer (Scheme 1).…”

“…Interestingly, the protonation of isostructural phosphanides 2-4 resulted exclusively in the formation of trans 1. We assume that this selectivity most likely originated from the preferential attack of water from the metal side for kinetic reasons, since the energy difference between cis and trans 1 was only small in favor of the trans isomer (0.1 kcal/mol at the B3LYP/6-311+G** level of theory) [10]. Inorganics 2018, 6, x FOR PEER REVIEW 5 of 9 Ellipsoids were drawn at the 30% probability level.…”

“…Compared with the parent hydrophosphane, 1, the formal phosphanide centers in deprotonated 2-4 were more shielded with respect to cis 1, but deshielded with respect to trans 1. The adjacent phosphorus atoms were shifted downfield upon interaction with the alkali-metal cations (δ( 31 P): [10]. In turn, the additional electron pair at the formal phosphanide center in 2-4 increased the interaction compared with trans 1 [29,30].…”

“…In a similar vein, unsaturated phosphorus-rich phosphanides were employed as building blocks for remarkable supramolecular architectures at the limits of molecular chemistry [7][8][9]. Based on our own efforts in the chemistry of phosphorus-rich ferrocenophanes, we became interested in exploring the metallation of a P-H functionalized bridging unit in a fully phosphorus-bridged [3]ferrocenophane [10][11][12][13]. Herein, we report the results of our investigation targeting the metallation of a stereochemically predefined secondary triphosphane constrained by the [3]ferrocenophane scaffold.…”