Müller's hydrocarbon is a well-known open-shell singlet diradicaloid,yet its structural determination and redox property remain elusive due to its extremely high reactivity.Herein,we report the successful syn...Müller's hydrocarbon is a well-known open-shell singlet diradicaloid,yet its structural determination and redox property remain elusive due to its extremely high reactivity.Herein,we report the successful synthesis and full characterizations of the first neutral boron-centered analogue(4)of Müller's hydrocarbon,along with the first dianionic boron-centered analogue(5^(2−))featuring three isolable redox states.In the presence of two equivalents of N-heterocyclic carbene(NHC),reduction of 4,4”-bis(triisopropylphenylbromoboryl)terphenyl 3 with potassium graphite afforded NHC-stabilized boryl diradicaloid 4 with a near-pure diradical character(y0=0.93).Stepwise reductions of 4,4”-bis(dimesitylboryl)terphenyl 5 in THF yielded the isolable monoradical anion 5·−and diradical dianion 5^(2−),respectively,accompanied by a decreasing aromaticity within the conjugated spacer.Experimental studies and theoretical analyses revealed that both 4 and 5^(2−)exhibit large spin distributions at boron atoms,open-shell singlet ground states,and small singlet-triplet energy gaps.展开更多
基金support from the National Natural Science Foundation of China(22371197 and 22001184)Natural Science Foundation of Jiangsu Province(BK20200849).
文摘Müller's hydrocarbon is a well-known open-shell singlet diradicaloid,yet its structural determination and redox property remain elusive due to its extremely high reactivity.Herein,we report the successful synthesis and full characterizations of the first neutral boron-centered analogue(4)of Müller's hydrocarbon,along with the first dianionic boron-centered analogue(5^(2−))featuring three isolable redox states.In the presence of two equivalents of N-heterocyclic carbene(NHC),reduction of 4,4”-bis(triisopropylphenylbromoboryl)terphenyl 3 with potassium graphite afforded NHC-stabilized boryl diradicaloid 4 with a near-pure diradical character(y0=0.93).Stepwise reductions of 4,4”-bis(dimesitylboryl)terphenyl 5 in THF yielded the isolable monoradical anion 5·−and diradical dianion 5^(2−),respectively,accompanied by a decreasing aromaticity within the conjugated spacer.Experimental studies and theoretical analyses revealed that both 4 and 5^(2−)exhibit large spin distributions at boron atoms,open-shell singlet ground states,and small singlet-triplet energy gaps.
