4184
derivatized phosphate group at (2-2’. Ion 1 (mle 103) is also observed, reflecting the absence of the phosphate group at C-5’. Similarly, in 3 ’,5/-cyclic AMP-(TMS)3,aei, j, and k are unshifted from Figure Ib, while m and 1 are absent, A peak having no counterpart in 5 ‘-AMP is present at m/e 3 10, due to carbons 1, M = Co, V; 2, Ni(RPhHR&; X = 0 Ni(RSPhHR&; X = S x=o,s C-2’ through (2-5’ of the ribose skeleton, plus their substituents, including the cyclic phosphate trimethylcis (facial) and trans (meridianal) isomers are possible silyl ester. for complexes 1 with X = 0, R # CH3,*s3or X = S . Mass spectra of the TMS derivatives of the b a ~ e s ~ ~Equilibrium ,~ constants for the trans e cis reaction of are simple, consisting mainly of M and M - 15,12 tris(P-diketonato)metal(III) complexes are considerably reflecting the resistance of the aromatic nucleus toward less than statistical,2 indicating preferential stability of fragmentation.l3 While of little use in a detailed the trans form. In sharp contrast, pmr studies of trisstructural sense, their spectra appear well suited for (P-thioketonato)cobalt(III) complexes (CDC13, -30”) analytical applications. l 4 reveal exclusive population of the cis isomer for species The uncommon elemental compositions of nucleotide, with R = CH3,4Ph, bPr, t-Bu; one a-CH3 or P-H signucleoside, and base TMS derivatives make their highnal is observed consistent with C3 (or C,,) symmetry. resolution mass spectra amenable to computer-based Similarly, only the cis isomer was detectable in an identification techniques. We are currently exploring analogous series of V(II1) complexes (R = CH,, Ph, the direct analysis of nucleic acid hydrolysates in this i-Pr) whose lability ensures equilibrium isomer distribumanner, l5 based on the TMS derivatives described tions and whose large contact shifts minimize the possiabove. bility of accidental chemical shift degeneracy and an incorrect structural assignment. 3 4 Chemical shift data (12) For example, % 2 values for M and M - 15: uracil-(TMS)t, 91 17; thymine-(TMS)t, 8, 17; cytosine-(TMS)z, 10, 12; adenine-(TMS)z, for a typical pair of tris(0-thioketonates) (R = Ph) 9, 30; guanine-(TMS)r,7, 18. are the following: a-CH3, - 141, -4193; P-H, -395, (13) See, for instance: (a) H. Budzikiewicz, C. Djerassi, and D . H. - 3507 cps (Co(III), V(III), TMS reference). Heating Williams, “Mass Spectrometry of Organic Compounds,” Holden-Day, Inc., San Francisco, Calif., 1967, pp 585, 592; (b) J. M. Rice and G. 0. the thio V(II1) complex with R = i-Pr in CDCI3 for Dudek, J . Am. Chem. SOC.,89,2719 (1967). 24 hr at 118” produced no trans rearrangement. (14) P. M. Krueger and J. A. McCloskey, unpublished experiments. (15) D . M. Desiderio, N. R. Earle, P. M. Krueger, A. M. Lawson, Preferential cis stability may arise in part from nonL. C. Smith, R. N. Stillwell, K. Tsuboyama, J. Wijtvliet, and J. A. bonded S...S interactions in the Sa unit, similar t o McCloskey, Sixteenth Annual Conference on Mass Spectrometry and those which may assist stabilization of trigonal prisAllied Topics, Pittsburgh, Pa., May 1968. (16) Recipient of a Robert A. Welch Foundation Postdoctoral Felmatic coordinationV6 lowship. The dynamic planar ~2 tetrahedral equilibrium has (17) Postdoctoral fellowship support through the National Institutes been demonstrated for Ni(R-PhHRJ2 (R, = H, CH3) of Health (Grant 5 TO1 HE 05703) is gratefully acknowledged. in noncoordinating solvents and thermodynamic data James A. McCloskey, A. M. Lawson16 derived from analysis of the temperature dependence K. Tsuboyama, P. M. Krueger,” R. N. Stillwell of the contact Analogous thio complexes Institute f o r Lipid Research and Department of Biochemistry (R, = H), an unexplored group of compounds,lO were Baylor University College of Medicine, Houston, Texas 77025 prepared by nonaqueous chelation7 employing 8Receiaed April 19, 1968 aminothiones obtained by the reaction of 3-phenyl1,2-dithiolium perchlorate12 with primary amines. For Comparative Stereochemical Effects of Sulfur and Ni(t-Bu-SPhHH)z close correspondence of solution Oxygen Donor Atoms in Four- and Six-Coordinate (3.18 BM, CHC13)and solid-phase (3.20 BM) magnetic Metal Complexes moments indicates that, like N ~ ( ~ - B U - P ~ Hthe H)~ mole ,~ ( N t ) is equal to 1 in solufraction of tetrahedral form Sir : tion. For both, -AFaWo >2.8 kcal/mole and no In complexes of potentially variable stereochemistry, sterochemical differences are observable. However, observations from a rapidly growing body of evidence for the pairs Ni(R-SPhHH),-Ni(R-PhHH)z, R = Amp indicate that unsaturated, sulfur-containing, chelating (CH3CHCH2Ph),sec-Bu, the equilibrium positions in ligands may induce preferential stability of structures carbon tetrachloride or chloroform solution are such which are either unusual or of widespread occurrence. that detectable amounts of both stereoisomers of all Pertinent examples include the planar structures of bis(2) R. C. Fay and T. S. Piper, J . Am. Chem. SOC.,84, 2303 (1962); dithiolene complexes with a variety of metal ions and 85,500 (1963). (3) F. Rijhrscheid, R. E. Emst, and R. H. Holm, Inorg. Chem., 6. the trigonal prismatic structures of certain trisdithio1315 (1967). lenes. 1 Particular stereochemical consequences of sul(4) See also A. Yokoyama, S. Kawanishi, M. Chikuma, and H. fur donor atoms are most clearly recognized and asTanaka, Chem. Pharm. Bull. (Tokyo), 15, 540 (1967). (5) F. Rohrscheid, R. E. Ernst, and R. H.Holm, Inorg. Chem., 6, sessed by structural comparisons with complexes identi1607 (1967); J . Am. Chem. SOC.,89, 6472 (1967). cal in constitution except for the donor atom sets. (6) R. Eisenberg and H. B. Gray, Inorg. Chem., 6,1844 (1967). Here are presented two structural comparisons: one (7) G. W. Everett, Jr., and R. H. Holm, J . Am. Chem. Soc., 87, 21 17 (1965); 88,2442 (1966). of a qualitative nature for six-coordinate complexes (8) G. W. Everett, Jr., and R. H. Holm,Inorg. Chem., 7.776 (1968). (l),and the other quantitative for four-coordinate com(9) R. E. Ernst, M. J. O’Connor, and R. H.Holm, J. Am. Chem. SOC., 89, 6104 (1967). plexes (2), which reveal the relative stereochemical (10) Only several examples have been reported; cf. E. Uhlemann, Z. effects of sulfur vs. oxygen donor atoms. Naturforsch., Zlb, 592 (1966). (1) A. L. Balch, I. G. Dance, and R. H. Holm, J. Am. Chem. SOC.. 90, 1139 (1968), and references therein; J. A. McCleverty, Progr. Inorg. Chem., in press.
Journal of
the
American Chemical Society / 9O:lS
(11) D. Leaver, D. M. McKinnon, and W. A. H. Robertson, J . Chem. SOC.,32, (1965). (12) E.Klingsberg, J. Am. Chem. SOC.,83.2934 (1961).
July 17, 1968
4185 complexes are present over the entire temperature range of contact shift measurements (240-360°K). Active [(+,+), (-,--)I and meso (+,-) diastereoisomers are generated by the two asymmetric ligand centers; as in other casesg*13their pmr signals are clearly resolved and identifiable by preparation of active isomers from resolved amines. Thermodynamic data for comparison, obtained by a procedure described9 using P-H signals and hyperfine coupling constants (aSH)from the R = t-Bu complexes, are presented in Table I. Two important conclusions
Restricted Rotation Aromd Phosphorus-Nitrogen Bonds' Sir: We wish to report the first measurement of a rotational barrier around a P-N bond. The 'H nmr spectrum of chloro(dimethy1amino)phenylphosphine (l), CsHsP(C1)N(CHa)2,displayed the expected doublet in the methyl region at ambient temperature with J p N c H = 12.6 Hz and 7 7.4.2 On cooling, the methyl doublet broaded (Figure 1b) and eventually coalesced. Below
Table I. Thermodynamics of the Planar-Tetrahedral Structural Conversion of Nickel(I1) Complexes 2 (X = 0, S) in Carbon Tetrachloride Solution. ~~
~~
AH, Pair
call Isomer mole
AF8210,
AS, eu
call mole
1,
N t a a s 0*
-320 3.06 -1310 3580 11.4 -98
0.89 0.54
Ni(AmpPhHH)z Ni(AmpSPhHH)s
399 4.70 -1120 2910 11.4 -784
0.85 0.77
Ni(sec-Bu-PhHHh Ni(sec-Bu-SPhHH)z active
892 5.98 -1040 3490 10.1 221
0.83 0.41
Ni(sec-Bu-PhHHh Ni(sec-Bu-SPhHH)t
1230 3120
0.82 0.54
Ni(AmpPhHH)2
A Ni(AmpSPhHHh active
6.82 9.98
-969 -106
la
I
Data calculated from measured proton contact shifts (240~ S H (X = 0) = -0.884 G (from Ni(t-Bu-PhHH)z) and apH (X = S) = -0.717 G (from Ni(t-BuSPhHH)S. Given at the indicated temperature for comparison with data in ref 9.
360°K) and eq 3 in ref 9 using
applicable within and below the temperature interval of measurement emerge for the pairs A-D compared: (i) AFs - AFo = A A F > 0, demonstrating that sulfur effects greater stabilization of planar stereochemistry than oxygen; (ii) lAAH1 > ITAASI, indicating that inequalities in stereochemical populations are due to enthalpy rather than entropy effects. On the basis of arguments developed elsewhere,8 differences in metalligand bonding in the two stereoisomers are considered principally responsible, with a large extent of T bonding in the planar thio complexes a plausible source of the stability differences. Comparison of experimental and calculated spin densities, currently underway, should serve to establish relative degrees of T bonding in the tetrahedral 0, S stereoisomers. Finally, conclusions i and ii are unchanged by comparisons in CDCla solutions, the following A A F = A A H - TAAS relationships having been obtained for the indicated pairs: A, 5060 - 12.0T; B, 3960 - 11.5T; C, 3900 - 8.OT; D, 3250 - 7.2T. Acknowledgment. This research was supported by National Science Foundation Grant GP-7576X. (13) R. H. Holm, A. Chakravorty, and G. 0. Dudek, J . Am. Chem. R. E. Ernst, M. J. O'Connor, and R. H. Holm,
SOC.,86, 397 (1964); ibid., in press.
(14) National Science Foundation Predoctoral Fellow 1966 to present.
R. H. Holm, D. H. Gerlach, J. G.Gordon, II," M. G. McNamee Department of Chemistry, Massachusetts Institute of Technology Cambridge, Massachusetts 02139 Received May 24, I968
*
5
-
-
L 55O
Ib IC IC
Id
I
I
6
7
I
I
8
9
7
Figure 1.
-60" (Figures Id, e) two clearly defined doublets developed. At -80' the low-field doublet (7 7.22) had JPNCH = 19.2 Hz and the high-field doublet (7 7.75) had (1) This work was supported by the Air Force Office of Scientific Research, through Grant No. AF-AFOSR-1050-67, and the Robert A. Welch Foundation. (2) All spectra were measured by Mr. E. J. Burshnick on a Varian Associates HA-100 spectrometer equipped with a calibrated variabletemperature accessory. Approximately 15% solutions of the (dialkylamino)phosphines in CClaF were sealed in uucuo along with a few per cent TMS as internal standard. Chloro(dibenzy1amino)phenylphosphine was dissolved in CDCls (5 solution) with CHzClr internal standard.
Communications to the Editor
