Ambiphilic Behavior of Ge(II)-Pseudohalides in Inter- and Intramolecular Frustrated Lewis Pair Alkyne Addition Reactions.

The reaction of the germylene chloride (NacNac)GeCl ( 1 , NacNac = CH{(CMe)(2,6- i Pr 2 C 6 H 3 N)} 2 ), phenylacetylene, and B(C 6 F 5 ) 3 gives the intermolecular frustrated Lewis pair (FLP) addition product 2 . In this case, the Ge(II) center acts as a base. In contrast, the analogous reaction of germylene thiocyanate 3 reacts independently with B(C 6 F 5 ) 3 to give the germylene cation salt [(NacNac)Ge][SCNB(C 6 F 5 ) 3 ] 4 . Subsequent in the presence of alkynes, the Ge(II) cation and γ-C of 4 act as a Lewis acidic and basic center, respectively, to affect the addition of alkynes, affording products [(NacNac)Ge(RCCR')][SCNB(C 6 F 5 ) 3 ] 5 and 6 . Compound 4 also reacts with Me 3 SiCN to give the cyanide-bridged Ge/B species 7 , which also reacts with phenylacetylene to give CN abstraction and intramolecular addition yielding the salt [(NacNac)Ge(PhCCH)][NCB(C 6 F 5 ) 3 ] 8 . Despite the similarity of 1 and 3 , DFT calculations show that the highest occupied molecular orbital (HOMO) of 1 is mainly located at the more sterically hindered germylene center, while the HOMO of 3 is located on the less sterically hindered NCS group, prompting markedly different FLP addition products.