704 Table I. Partial Resolutiona of Ni(ruc-l,7-CT)(NCS)t Fraction 1 2 3 5 7 10 13 14
Concn, g/ml
degbtE +O. 264 +o. 559 +O. 745 $0.139 -0.210 -0,102 -0.052 -0.069
(Yobsd,
9.95 20.4 32.9 34.6 25.7 5.9 3.1 3.8
x
104 d
tal^ d a d +133 +137 +113 20 - 41 - 87 - 83 - 90
+
This resolution was achieved chromatographically using a column packed with potato starch and 0.01 N HC1 as the eluent. * Readings Standard deviation of values &0.008". d Determined spectrophotometritaken with a Rudolph Model 80 polarimeter using a 2-dm tube. cally. c Uncertainty -&So. Q
proof, the resolution of dl-Ni( 1,7-CT)(NCS)%is significant as a novel example of optical activity due to the nitrogens of coordinated secondary amine^.^
'
I
Ji/ I
/I'
Figure 2. Pmr spectra of Ni(CT)(NCS)2isomer's: (a) Ni(l,4-CT)(NCS)? in neutral DzO; (b) N ~ ( ~ U C - ~ , ~ - C T ) (in NC acidic S ) ~ D20; (c) Ni(meso-l,7-CT)(NCS)? in acidic D2O. Spectra calibrated in ppm downfield from external TMS.
Both pmr and visible spectra demonstrate that both pure Ni(mes0-1,7-CT)~+and pure Ni(r~c-1,7-CT)~+ convert to the same equilibrium mixture of isomers in neutral aqueous solution or in acetone. However, if the solutions are distinctly acidic, the isomerization process is stopped. This is consistent with the long known pH dependence of hydrogen-exchange reactions involving coordinated amine groups.'j When separated from chloroform, Ni(meso-l,7-CT)(NCS)2 crystallizes with coordinated thiocyanates. Its spectrum and magnetic moment (3.2 BM) are typical of pseudo-octahedral nickel(II).' It is apparent (Figure 1) that the two extraplanar coordination sites are equivalent in the Ni(mes0-1,7-CT)~+, but not in the rac- 1,7-CT complex. The paramagnetic violet isomer is unstable and readily converts into the yellow diamagnetic form. It is instructive to consider the only known (diamagnetic) isomer of Ni(1,4-CT)2+ along with the Ni( 1,7-CT)2+ isomers. Three equally intense methyl resonances are most prominent in the pmr spectra (Figure 2) of all isomers: for NCS- salts, Ni(rac-1,7CT)2+, 2.67, 2.52, and 1.75 ppm; Ni(mes0-1,7-CT)~+, at 2.69, 2.21, and 1.75 ppm; and Ni(1,4-CT)2+, 2.70, 2.54, and 1.75 ppm. Three resonances require the six methyl groups to be pairwise equivalent, a result easily accommodated if the two six-membered chelate rings ( 5 ) Subsequent to submission of this report, the first convincing
example of optical activity in a coordinated secondary amine appeared: B. Halpern, A. M. Sargeson, and I----p-Silyl ketone
60 (78-80) 41 (80.5-82.0) 48b 24 (78-84 (1 1 mmc)) 33d 33d 33 (oil)
Ph pClc~H4 pMeOCsH4 Ph Ph Ph Phe Me Me Ph
40 (88-90) 59 (121-121.5) 52 (101-102) 76 (104 (3.1 mm)) 67 (117-118.5) 66 (149-151) 67 (54-56) 670 820 810 (81-83)
f
a Relative yields were determined from the relative intensities of the nmr proton signals. b Compound not actually isolated, except as pmethoxyacetophenone, the decomposition product. The /3-ketone was quite stable. c Compound slightly contaminated with phenacyltrimethylsilane. d Compound not isolated, except as acetophenone, the decomposition product, The p-ketone was quite stable. e Optically active enantiomer used. f The nrnr spectrum of the first fraction eluted from silica gel with chloroform indicated that a small amount Pure isolated material. h Under the experimental conditions (2-3 weeks (
