Carbenes as Electron-Pair Donors for P⋅⋅⋅C Pnicogen Bonds

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Non-covalent Interactions

Background:

• Pnicogen bonding is an important non-covalent interaction involving Group 15 elements.
• Carbene molecules are reactive intermediates with unique electronic properties.
• Understanding the interplay between pnicogen bonding and carbene structures is crucial for predicting chemical reactivity and designing new molecules.

Purpose of the Study:

• To investigate the structural and electronic properties of pnicogen-bonded complexes formed between H2XP molecules (X=F, Cl, NC, OH, CH3, CN, CCH, H) and singlet carbene molecules: C(NH2)2, C(OH)2, and cyclic C(OCH)2 [OHC].
• To elucidate the nature of the interactions, including covalent P-C bonds, P...C pnicogen bonds, O-H...P hydrogen bonds, and P...π bonds.
• To analyze the influence of substituents on the phosphorus atom and the carbene structure on the complex formation and stability.

Main Methods:

• Ab initio MP2/aug'-cc-pVTZ calculations were employed to model the electronic structure of the complexes.
• Analysis of binding energies, charge-transfer energies, and electron density properties was performed.
• Equation-of-motion coupled cluster singles and doubles (EOM-CCSD) spin-spin coupling constants were calculated to probe bonding characteristics.

Main Results:

• Two distinct structures (coplanar and non-coplanar) were identified for H2XP:C(NH2)2 and H2XP:C(OH)2 complexes, with their formation depending on the electronegativity of the substituent X.
• H2XP:C(NH2)2 and H2XP:C(OH)2 complexes are stabilized by P-C covalent bonds or P...C pnicogen bonds, while some coplanar complexes are stabilized by O-H...P hydrogen bonds.
• H2XP:OHC complexes exhibit non-coplanar structures stabilized by P-C covalent bonds or pnicogen bonds, and in some cases, by P...π interactions.

Conclusions:

• The nature of bonding and the preferred geometry of pnicogen-bonded carbene complexes are highly sensitive to the electronic properties of both the phosphorus-containing molecule and the carbene.
• This study provides a comprehensive understanding of various non-covalent interactions governing the assembly of these complexes.
• The findings contribute to the fundamental knowledge of chemical bonding and can guide the design of novel materials and catalysts.