Even the normal is abnormal: N-heterocyclic carbene C(2) binding to a phosphaalkene without breaking the P[double bond, length as m-dash]C π-bond.
Majhi, Paresh Kumar; Chow, Keith C. F.; Hsieh, Tom H. H.; Bowes, Eric G.; Schnakenburg, Gregor; Kennepohl, Pierre; Streubel, Rainer; Gates, Derek P.; Chemical communications (Cambridge, England) 52 (2016) 998–1001; doi:10.1039/c5cc08181e

data_7118345
_publ_section_title
;
 Even the normal is abnormal: N-heterocyclic carbene C(2) binding to a
 phosphaalkene without breaking the P[double bond, length as m-dash]C
 \p-bond.
;
_journal_issue                   5
_journal_name_full
'Chemical communications (Cambridge, England)'
_journal_page_first              998
_journal_page_last               1001
_journal_paper_doi               10.1039/c5cc08181e
_journal_volume                  52
_journal_year                    2016
_chemical_formula_moiety         'C29 H33 N2 P'
_chemical_formula_sum            'C29 H33 N2 P'
_chemical_formula_weight         440.54
_chemical_name_systematic        PKM-VAN-1
_space_group_crystal_system      monoclinic
_space_group_IT_number           14
_space_group_name_Hall           '-P 2ybc'
_space_group_name_H-M_alt        'P 1 21/c 1'
_symmetry_space_group_name_Hall  '-P 2ybc'
_symmetry_space_group_name_H-M   'P 1 21/c 1'
_atom_sites_solution_hydrogens   geom
_atom_sites_solution_primary     direct
_audit_creation_date             2015-06-16
_audit_creation_method
;
Olex2 1.2
(compiled 2015.01.26 svn.r3150 for OlexSys, GUI svn.r4998)
;
_audit_update_record
;
2015-09-28 deposited with the CCDC.
2015-11-16 downloaded from the CCDC.
;
_cell_angle_alpha                90
_cell_angle_beta                 102.838(13)
_cell_angle_gamma                90
_cell_formula_units_Z            4
_cell_length_a                   11.3578(19)
_cell_length_b                   9.9307(13)
_cell_length_c                   22.539(5)
_cell_measurement_reflns_used    2682
_cell_measurement_temperature    100
_cell_measurement_theta_max      29.31
_cell_measurement_theta_min      2.30
_cell_volume                     2478.6(8)
_computing_cell_refinement       'SAINT v8.34A (Bruker, 2013)'
_computing_data_reduction        'SAINT v8.34A (Bruker, 2013)'
_computing_molecular_graphics    'Olex2 (Dolomanov et al., 2009)'
_computing_publication_material  'Olex2 (Dolomanov et al., 2009)'
_computing_structure_refinement  'ShelXL (Sheldrick, 2008)'
_computing_structure_solution    'ShelXS (Sheldrick, 2008)'
_diffrn_ambient_temperature      100
_diffrn_detector_area_resol_mean 8
_diffrn_measured_fraction_theta_full 0.997
_diffrn_measured_fraction_theta_max 0.995
_diffrn_measurement_device_type  'Bruker X8-KappaApexII'
_diffrn_measurement_method       'fine slicing \w and \f scans'
_diffrn_radiation_monochromator  graphite
_diffrn_radiation_type           MoK\a
_diffrn_radiation_wavelength     0.71073
_diffrn_reflns_av_R_equivalents  0.0752
_diffrn_reflns_av_unetI/netI     0.0864
_diffrn_reflns_laue_measured_fraction_full 0.997
_diffrn_reflns_laue_measured_fraction_max 0.995
_diffrn_reflns_limit_h_max       14
_diffrn_reflns_limit_h_min       -15
_diffrn_reflns_limit_k_max       13
_diffrn_reflns_limit_k_min       -13
_diffrn_reflns_limit_l_max       28
_diffrn_reflns_limit_l_min       -29
_diffrn_reflns_number            21757
_diffrn_reflns_point_group_measured_fraction_full 0.997
_diffrn_reflns_point_group_measured_fraction_max 0.995
_diffrn_reflns_theta_full        26.000
_diffrn_reflns_theta_max         27.999
_diffrn_reflns_theta_min         2.755
_diffrn_source                   'sealed tube'
_diffrn_standards_number         0
_exptl_absorpt_coefficient_mu    0.130
_exptl_absorpt_correction_T_max  0.7459
_exptl_absorpt_correction_T_min  0.5954
_exptl_absorpt_correction_type   empirical
_exptl_absorpt_process_details
;
SADABS-2014/5 (Bruker,2014/5) was used for absorption correction.
wR2(int) was 0.1214 before and 0.0790 after correction.
The Ratio of minimum to maximum transmission is 0.7982.
The \l/2 correction factor is 0.00150.
;
_exptl_crystal_colour            'clear red'
_exptl_crystal_colour_lustre     clear
_exptl_crystal_colour_primary    red
_exptl_crystal_density_diffrn    1.181
_exptl_crystal_description       block
_exptl_crystal_F_000             944
_exptl_crystal_size_max          0.1
_exptl_crystal_size_mid          0.08
_exptl_crystal_size_min          0.05
_refine_diff_density_max         0.272
_refine_diff_density_min         -0.443
_refine_diff_density_rms         0.063
_refine_ls_extinction_method     none
_refine_ls_goodness_of_fit_ref   1.006
_refine_ls_hydrogen_treatment    constr
_refine_ls_matrix_type           full
_refine_ls_number_parameters     296
_refine_ls_number_reflns         5947
_refine_ls_number_restraints     0
_refine_ls_restrained_S_all      1.006
_refine_ls_R_factor_all          0.0909
_refine_ls_R_factor_gt           0.0462
_refine_ls_shift/su_max          0.001
_refine_ls_shift/su_mean         0.000
_refine_ls_structure_factor_coef Fsqd
_refine_ls_weighting_details
;
 w=1/[\s^2^(Fo^2^)+(0.0512P)^2^]
 where P=(Fo^2^+2Fc^2^)/3
;
_refine_ls_weighting_scheme      calc
_refine_ls_wR_factor_gt          0.1023
_refine_ls_wR_factor_ref         0.1218
_reflns_Friedel_coverage         0.000
_reflns_number_gt                3909
_reflns_number_total             5947
_reflns_threshold_expression     'I > 2\s(I)'
_cod_data_source_file            c5cc08181e2.cif
_cod_data_source_block           4149f
_cod_database_code               7118345
_shelxl_version_number           2013-2
_shelx_estimated_absorpt_t_max   0.994
_shelx_estimated_absorpt_t_min   0.987
_olex2_refinement_description
;
1. Fixed Uiso
 At 1.2 times of:
  All C(H) groups
 At 1.5 times of:
  All C(H,H,H) groups
2.a Aromatic/amide H refined with riding coordinates:
 C3(H3), C5(H5), C19(H19), C20(H20), C21(H21), C22(H22), C23(H23), C25(H25),
 C26(H26), C27(H27), C28(H28), C29(H29)
2.b Idealised Me refined as rotating group:
 C7(H7A,H7B,H7C), C8(H8A,H8B,H8C), C9(H9A,H9B,H9C), C13(H13A,H13B,H13C),
 C14(H14A,H14B,H14C), C15(H15A,H15B,H15C), C16(H16A,H16B,H16C)
;
_shelx_res_checksum              84810
_olex2_submission_special_instructions 'No special instructions were received'