Is it permissible for a manager to contract with suppliers for his private account after contracting with them on behalf of the company, even though this is not among his primary duties?

If you searched for suppliers as a company manager and on behalf of the company and contracted with them on that basis, it is not permissible to exploit that for your personal benefit. However, if you searched for suppliers outside the scope of the company, it is stipulated that this should not harm your working hours, that you should not favor suppliers at the expense of the company, and that you should not contract with them for your personal account if there is a possibility of breaching these conditions. There is no harm in dealing with suppliers for your personal account if the contracting party for the supply contracts is independent and neutral, and has a separate supervisory body that is not subject to your management, to avoid the suspicion of exploiting the company.