Stericaliy Congested Molecules: 2,2′‐[(Biaryldiyl)bis(oxy)]bis[1,3,2‐oxazaphospholidines]

Abstract

The original suggestion that a through‐space mechanism was operative in the seven‐bond J(P, P) coupling constant of 30.3 Hz observed for 3.3′‐bis(1,1‐dimethylethyl)‐2,2′‐[3,3′,5,5′‐tetrakis(1,1‐dimethylethyl)‐1,1′‐biphenyl‐2,2′‐diyl]bis(oxy)}bis[1,3,2‐oxazaphospholidine] (1a)) was investigated. In the solid‐state CP‐MAS 31PNMR spectrum of 1a, two nonequivalent P‐atoms were observed; sufficient resolution could not be obtained to determine whether P, P coupling was present. The preparation and spectral data of the N‐methyl analogue 1b and of the acyclic N‐isopropyl analogue 6 (Scheme 1) provided evidence that a) the essentially exclusive formation (R*, R*,S*)‐1ain the reaction of the disodium biphenyldiolate 3a with the phosphorochloridite 4a is the result of significant differences in the free energy of activation (ΔG*) for the formation of the various diastereoisomers due to the steric congestion within the molecule and that b) the magnitude of the observed P,P coupling is dependent upon the degree of conformational freedom within the molecule. In the 31P‐NMR spectrum of the P‐sulfide 7, which was prepared by the reaction of la with sulfur, 2s resonances were observed that strongly suggested that the lone electrons pair on P are involved in the mechanism for the transmission of coupling data. The (4S,5R)‐12 and (4R, 5S)‐12 of la were prepared in a three‐step reaction sequence starting from the corresponding enantiomerically pure norephredine 8 (Scheme 2). Both (4S, 5R)‐ and (4R, 5S)‐12 were obtained as a diastereoisomer mixture that differ by the configuration of the axis of chirality, i.e., (R*R*,R*)‐ and (R*,S*,R*)‐12 were obtained. The major diastereoisomer was obtained upon recrystallization, and the atropisomers were observed to equilibrate in solution by monitoring the HC(5) resonance in the 1H‐NMR with time (ΔG° = 0.4 kcal/mol; Fig. 2). The process observed corresponds to the restricted rotation about the central single bond of the biphenyl system. The isolation of an atropisomer with only a single ortho substituent on each aryl ring is quite rare. In the 13C‐NMR spectrum of both (R*,R*,R*)‐ and (R*,S*,R*)‐12, C(5) is two‐bond‐coupled to the oxazaphospholidine P‐atom (2J(C(5),P((2)) = 8.5 Hz) that is further virtually coupled to the P‐atom of the other oxazaphospholidine ring (7J(P(2),P(2′)) = 30 Hz; 9J(C(5),P(2′)) = 0 Hz; δ(P(2)) = δ(P(2′)) = 136 ppm. In the 31P‐NMR spectrum of (R*,R*,S*)‐12, which was prepared from the racemic chloridite (mixture of three diastereoisomers was obtained), a 7J(P(2),P(2′) of 36 Hz was observed. These observations provide strong evidence that seven‐bond P,P coupling occurs in all three diastereoisomers of 12. The observed P,P coupling is both independent of the configuration of the chiral axis and the configuration of the asymmetric P‐centers. This independence of P,P coupling upon the configuration on P implies also the independence of the observed coupling upon the orientation of the lone‐pair of electrons on P provided that the conformations of the diastereoiso...

Diastereomeric P*-mono- and P*,P*-bidentate diamidophosphite ligands based on 1,4:3,6-dianhydro-d-mannitol in asymmetric metallocomplex catalysis

“…The allylic amination of 19 by pyrrolidine using the [Pd(All)Cl] 2 /(S C ,R P ) 4 catalytic system or isolated complex (S C ,R P ) 10 occurs with the quantitative conversion and high enantioselectivity for product (R) 23 (87-95%, Table 4, entries 5-10) regard less of the L/Pd molar ratio and nature of the solvent. Under the same conditions, (R C ,S P ) 4 provides lower con version (in THF) and enantioselectivity (ee 66-79% for (S) 23, Table 4, entries [11][12][13][14][15][16]. Similarly P* monoden tate diamidophosphite (S C ,R P ) 5 is a better stereoselector than its "unnatural" diastereomer (R C ,S P ) 5: (R) 23 and (S) 23 are formed with enantioselectivities up to 92 and 80%, respectively (Table 4, entries 17-28).…”

“…5-10 At the same time, only several promising P*,P* bidentate ligands of the phosphite type bearing stereogenic phosphorus atoms are described. [11][12][13] This is rather surprising, because it is well known 2 that ligands with asymmetric donor atoms are excellent stereoselectors.…”

STRUCTURAL ASPECT OF PLATINUM COORDINATION COMPOUNDS: PART III. MONOMERIC SQUARE PLANAR (Pt A2XY AND PtABXY) AND TRIGONAL BIPYRAMIDAL PtII COORDINATION COMPOUNDS

“…The cis-PtCl 2 (mtso) 2 molecule exists separately in two distortion isomeric forms [17,18] There are over one hundred and twenty PtCl 2 P 2 chromophores, five PtCl 2 Se 2 and one PtCl 2 As 2 in this group listed in Table 2. with four-membered chelate rings [106,107], five-membered [108][109][110][111][112][113][114][115][116][117][118], sixmembered [119][120][121][122][123][124][125][126][127], seven-membered [128][129][130][131][132][133][134], eight-membered [135,136], nine-membered [137,138], twelve-rnembered [139][140][141], fifteen-membered [142][143], seventeen-membered [144] and twenty-membered'metallocyclic rings [144,145]. For the remainder, bidentate P-donor ligands are involved, Chromophore.…”

Atomic Proximity Due to Molecular Congestion: Rational Design of Bis(phosphite) Ligands by Restriction of Molecular Motion1

“…Careful application of this strategy could be used, in principle, to design ligands that provide a defined coordination sphere about a metal for catalytic reactions. Application of this strategy to chiral bis(phosphite) ligands analogous to 4 , which contain both a stereoaxis and stereocenter, provides a model ligand to investigate the notion of internal cooperativity of chirality . − We report herein our progress in defining the effect of multiple tert -alkyl substitution on the conformational freedom of bis(phosphite) ligands.…”