Selected spectroscopic data for complexes prepared in this work, and some previously reported complexes for comparison.

Entry	Complex	13C δC-αa	13C δC-βa	13C δCOa	ν CO b (sym)	ν CO b (asym)	k CO c
2a	Co(CO)2(η5-AsC4Ph4)	137.2	135.1	203.8	2026	1978, 1970d	16.13
2b	Co(CO)2(η5-AsC4Ph2H2)	138.1	94.9	203.0	2032	1985, 1976d	16.23
2c	Co(CO)2(η5-AsC4Me4)	118.9e	113.1e	205.1e	2019	1967	16.02
2d	Co(CO)2(η5-AsC4Et4)	128.4e	118.8e	205.3e	2017	1965	15.99
2e	Co(CO)2{η5-AsC4(SiMe3)2Me2}	122.2e	119.8e	204.5e	2015	1962	15.95
2f	Co(CO){P(OMe)3}(η5-AsC4Me4)	114.3	109.8	206.8	1947		15.39
2g	Co(CO){P(OMe)3}(η5-AsC4Et4)	124.4	115.3	207.3	1945		15.36
2h	Co(CO){P(OMe)3}{η5-AsC4(SiMe3)2Me2}	118.7	116.1	205.5	1941		15.30
	Co(CO)2(η5-C5H5)11	84.5e		205.6e	2033f	1972f	16.17
	Co(CO)2(η5-C5Me5)11	96.7e		207.9e	2011	1949	15.81
	Co(CO)2(η5-C5Ph5)8	No data reported			2000	1945	15.69
	Co(CO)2(η5-C5{CH2Ph}5)8	No data reported			2020	1960	15.97
	Co(CO)2(η5-PC4Ph2H2)9	No data reported			2030	1980	16.21
	Co(CO)2(η5-PC4tBu2H2)10	136.2	91.9	204.0	2023	1968	16.06
	Co(CO){P(OMe)3}(η5-PC4tBu2H2)10	134.7	90.5	208.0	No data reported		—

^aC₆D₆ solution unless otherwise stated, ppm downfield from SiMe₄, 25 °C; the labels α and β refer to ring-carbon positions with respect to the heteroatom (where applicable).

^b n-Hexane solution unless otherwise stated, cm⁻¹, 25 °C.

^cCotton–Kraihanzel force constant in N cm⁻¹.

^dResolution of the doubly degenerate E vibrational mode is observed in n-hexane for these complexes cf., ν_CO (CH₂Cl₂): 2a 2022, 1963 cm⁻¹; 2b 2027, 1972 cm⁻¹.

^eCDCl₃ solution, 25 °C.

^fCyclohexane solution.