Group 14 metal terminal phosphides: correlating structure with |J(MP)|.

Area of Science:

• Organometallic Chemistry
• Main Group Chemistry
• Coordination Chemistry

Background:

• Group 14 elements (Ge, Sn, Pb) are foundational in inorganic and organometallic chemistry.
• Terminal phosphide complexes are crucial for understanding bonding and reactivity.
• The influence of ligand structure on coordination geometry and electronic properties is a key area of research.

Purpose of the Study:

• To synthesize and characterize novel heavier group 14 element terminal phosphide complexes.
• To investigate the conformational preferences (endo vs. exo) and their impact on phosphorus geometry.
• To explore the electronic communication and bonding characteristics through NMR spectroscopy, focusing on coupling constants.

Main Methods:

• Synthesis of group 14 phosphide complexes M(BDI)(PR2).
• Solid-state structural analysis to determine conformations (endo/exo) and coordination geometry.
• Solution-state Nuclear Magnetic Resonance (NMR) spectroscopy (1H, 13C, 31P, 119Sn, 207Pb) to probe electronic structure and through-space couplings.
• Variable temperature NMR studies to differentiate conformers.

Main Results:

• Successful synthesis of Ge, Sn, and Pb terminal phosphide complexes with a bulky BDI ligand.
• Observation of distinct endo and exo conformations, correlating with planar (sp2) and pyramidal (sp3) phosphorus hybridization, respectively.
• Significant differences in tin-phosphorus (|J(SnP)|) and lead-phosphorus (|J(PbP)|) coupling constants were observed, dependent on phosphorus hybridization and conformation.
• The largest reported |J(SnP)| value was achieved for Sn(BDI)(P{SiMe3}2), exceeding values typically associated with multiple bonds.
• Low-temperature NMR of the lead complex revealed two species with distinct |J(PbP)| values, confirming the presence of both endo (sp2 P) and exo (sp3 P) conformers.

Conclusions:

• The conformational preferences of heavier group 14 phosphide complexes are dictated by steric and electronic factors.
• Phosphorus hybridization (sp2 vs. sp3) significantly influences the magnitude of M-P coupling constants (|J(MP)|).
• The observed large |J(SnP)| values challenge traditional bonding models and suggest significant s-orbital character in the Sn-P interaction.
• NMR spectroscopy is a powerful tool for characterizing conformer populations and probing electronic structure in these systems.