Unusual coordination mode for 1,3-diphosphete ligands towards a Cr-Cr quintuple bond complex.

The reaction of LCr 5̲ CrL (L = N 2 C 25 H 29 , 1) with the phosphaalkynes R-C≡P (R = t Bu, Me, Ad) yields the neutral dimerisation compounds [L 2 Cr 2 (μ,η 1 :η 1 :η 2 :η 2 -P 2 C 2 R 2 )] (R = t Bu (2), Me (3)) and the tetrahedrane complex [L 2 Cr 2 (μ,η 2 :η 2 -PCAd)] (4). The 1,3-diphosphete ligands in complexes 2 and 3 are the first to possess this structural feature spanned over a metal-metal multiple bond, while the slightly bigger adamantyl phosphaalkyne remains a monomer in 4 with a side-on coordination mode.