1,4‐Diphosphabutadiyne: A Realistic Target for Synthesis? A Theoretical Investigation of C 2 P 2 , C 2 N 2 , [Cr(CO) 5 PCCP], and [(CO) 5 Cr(PCCP)Cr(CO) 5 ]

To assess the viability of 1,4‐diphosphabutadiyne (PCCP, 2 a ) as a target for synthesis, we have theoretically analyzed C 2 P 2 ( 2 ) and, for comparison, C 2 N 2 ( 1 ) isomers using nonlocal density functional theory. PCCP ( 2 a ) turns out to be thermodynamically stable, but it is likely to have a strong tendency toward polymerization. We have investigated terminal and side‐on complexes of 2 a as a conceivable strategy to protect and stabilize the evasive target molecule.