One objective of exploring the reactivity of dichromium complexes with proposed fivefold...

One objective of exploring the reactivity of dichromium complexes with proposed fivefold bonding is to obtain additional data to support these high bond orders

a. In this regard, [^HLi^PrCr]₂

with Ar = 2,6–diisopropylphenyl) (Figure 15.11(b)) reacts with internal alkyne to afford 1:1 adducts (J. Shen, G. P. A. Yap, J.-P. Werner, K.H. Theopold, Chem., Commun., 2011, 47, 12191). Does the product of the reaction with CH₃C CH₃ support a quintuple bond in the starting dichromium complex? Provide arguments on the basis of crystallographic data and calculated bond orders.

b. Reaction of [^HLi^PrCr]₂ with acetylene gives a product that has a Cr—Cr distance of 192.5 pm and a bridging HCCH ligand with a C—C distance of 132.6 pm (free acetylene has a C—C distance of 120.5 pm). Account for the increase in both Cr—Cr and C—C distances as the product is formed.